Inclusion Criteria:

run-in period: A subject will be considered eligible for the study only if all of the following criteria apply at start of placebo run-in period.

• Patients who are diagnosed with the following depressive disorders according to the DSM-IV-TR criteria, and currently presents with a depressive episodes. Depressive disorders: MDD, single episode (296.2), MDD, recurrent (296.3)
• 7 years and older and under 18 years old (at the time of consent obtained)
• Patients with a total raw summary score on the CDRS-R of 45 or greater at the Week -2 visit.
• Patients whose legally acceptable representative (e.g., caretaker, custodian) is able to give written consent to participation to this study. Patients aged 12 and above at the time of consent obtained should be able to sign the informed consent on one's own. Efforts should be exerted in obtaining the informed assent in writing from patients aged less than 12.
• Patients with ideal body weight +/- 2SD
• Gender: Male or female

treatment period:

Subjects who meet the following criteria at Week 0 (Baseline) may be progressed to the Treatment period:

- Patients with a total raw summary score on the CDRS-R at Week 0 visit of 45 or greater.

Exclusion Criteria

run-in period:

A subject will not be eligible for inclusion to this study if any of the following criteria applies at start of run-in period:

• Patients who in the investigator's judgment presented with a clinically predominant Axis I disorder other than MDD (e.g. dysthymic disorder, eating disorders, Specific phobia, PTSD, OCD, Panic disorder, etc)
• Patients with any history of a psychotic episode or psychotic disorder (including schizophrenia ), or complication of these diseases.
• Patients with a history of a bipolar disorder, or complication of these diseases.
• Patients with Attention-Deficit, or Hyperactivity Disorder
• Patients with Mental Retardation or Pervasive Development Disorder
• Patients diagnosed with Substance Abuse or Dependence within 12 weeks prior to the Screening visit
• Patients with past treatment experience with the investigational drug (i.e. paroxetine)
• Patients treated with electroconvulsive therapy in the immediate 12 weeks prior to the Screening visit
• Patients with past history of serotonin syndrome and neuroleptic malignant syndrome.
• Patients with CDRS-R score of "suicidal ideation" of 3 or greater. Or patients whose C-SSRS assessment suggests that they are or have been at significant risk for harming themselves or have actually harmed themselves, or who, in the opinion of the chief investigator (subinvestigator), are at significant risk for harming self.
• Patients with past history of suicide attempt, self harm(excluding "no suicidal intent " ), or an intentional overdose (excluding obviously unintentional overdose)
• Patients who have been treated with other clinical trial investigational drug (including post-marketing clinical trial) in the immediate past 3 months of the Week -2 visit.
• Patients who have taken antidepressant medication 1 week prior to screening.
• Patients with complicated disease of glaucoma.
• Patients with convulsive disorders such as epilepsy or past history of these diseases.
• Patients regularly using drugs (e.g. NSAIDs) that would increase the risk of haemorrhage, or patients with bleeding tendency or haemorrhagic diathesis.
• Patients with severe renal and hepatic disorder.
• Patients with serious organic disorder in the brain.
• Patients with chronic hepatitis type B and/or C which is positive of hepatitis B surface antigen (HBsAg) and/or hepatitis C antibody.
• Patients with a current history of carcinoma or malignant tumor, or complication of these diseases.
• Female patients who are pregnant, lactating, or who might be pregnant, or who wish to be pregnant during the study period
• Patients in the opinion of the chief investigator (subinvestigator) judged as not eligible for the study.
• Patients with clinical significant comorbid impulsivity symptoms.(e.g. Personality Disorder, Conduct Disorder)

treatment period: Subjects for whom any of the following categories apply at Week 0 (start of the treatment period) will not be progressed to the treatment phase.

• Patients with CDRS-R score of "suicidal ideation" of 3 or greater, or patients who, in the opinion of the chief investigator (sub investigator), are at significant risk for harming self
• Patients with variation of the CDRS-R total raw summary score at Week 0 of +/-25% or greater compared to that of Week -2.
• Patients with drug compliance of Drug 1 (run-in placebo) from Week -2 to Week 0 less than 80%.
• Patients, in the opinion of the chief investigator (sub investigator) judged as not appropriate for the study.