ROP
DrugRopinirole Hydrochloride monotherapy group (ROP): Patients will receive ROP tablets 3 times daily. In the 4-week Fixed Titration Phase (from Week 0 as Baseline), the dose will start at 0.75 mg/day and will be increased weekly by 0.75 mg/day up to 3.0 mg/day. In the 48-week Flexible Titration and Maintenance Phase, the dose will be increased by 1.5 mg/day at intervals of at least 1 week up to a maximum of 15.0 mg/day. The dose will be maintained at a level without further symptomatic improvement is expected. Concomitant use of L-dopa is prohibited during the study.