Inclusion Criteria:

• Patients who are diagnosed with PD with severity of the Modified Hoehn & Yahr staging at Stage I to III.
• Age: 20 years or older (at the time of giving informed consent)
• Gender: male and female
• Both inpatient and outpatient status
• Informed consent: Patients who are able to give informed written consent in person (i.e. patients who are capable of giving informed written consent on one's own)
• Limited prior exposure to low or moderate doses of L-dopa (up to 3 months in total) or dopamine agonists (up to 6 months in total) provided treatment is discontinued for a minimum of 4 weeks prior to screening.

Exclusion Criteria:

• Patients who present serious physical signs and symptoms other than those of the PD (e.g. cardiac/hepatic/renal disorder and haematopoietic disorder).

The seriousness refers to Grade 3 according to "the Classification of the Severity of Adverse Experiences (Pharmaceutical affairs bureau/Safety division (PAB/SD) Notification No. 80, dated 29 June 1992).

• Patients with symptomatic postural hypotension. (e.g. dizziness and syncope).
• Patients who have had serious psychiatric symptoms (e.g. confusion, hallucination, delusion, abnormal behaviour, alcohol or drug dependence) during the past six months (26 weeks) (including symptoms caused by anti-Parkinson drugs).

• Patients who have been treated with the following drugs at Week -4, and whose treatment regimen of the drug has been changed from Week-4 to Week0.

  • Anticholinergic agents: trihexyphenidyl hydrochloride (e.g. Artane®), piroheptine hydrochloride (Trimol®), mazaticol hydrochloride (Pentona®), metixene hydrochloride (Cholinfall®), biperiden hydrochloride (Akineton®), profenamine (Parkin®)
  • amantadine hydrochloride (e.g. Symmetrel®)
  • droxidopa (Dops®)
  • citicoline (e.g. Nicholin®)
  • selegiline hydrochloride (FP®)
  • zonisamide
  • estrogen: estriol (e.g.Estriel®)
  • CYP1A2 inhibitors: Ciprofloxacin HCl (e.g. Ciproxan®, enoxacin and fluvoxamine)
• Patients with severe dementia such as score 3 or 4 of the UPDRS Part I (Mentation, behaviour, and mood)
• Female patients who are pregnant or lactating, who may be pregnant, or who plan for pregnancy during the study or within 30 days after the last dose of the study drug.
• Patients with current history or complication of carcinoma or malignant tumour.
• Patients who have history of drug allergy to ropinirole hydrochloride (HCl).
• Patients who have received surgical treatment for PD in the past (e.g. pallidectomy, deep brain stimulation).
• Patients who have been treated with any other investigational drug within
• weeks prior to the treatment phase.
• Others whom the investigator (sub investigator) considers ineligible for the study.