A Study of KW-6356 in Subjects With Early Parkinson's Disease

Inclusion Criteria: * Subject fulfills the UK Parkinson's Disease Society brain bank clinical diagnostic criteria * Parkinson's disease patients in Stages 1 to 3 on the Modified Hoehn and Yahr Scale * MDS-UPDRS part III score of ≥ 15 Exclusion Criteria: * Use of any CYP3A4/5-related drugs within 2 weeks prior to enrollment. * Use of any of the specified antiparkinsonian drugs and dopamine antagonists during the specified period. * Treatment with levodopa/DCI at any time in the past for a period of 4 weeks or more. * Neurosurgical operation for Parkinson's disease (stereotactic surgery, deep brain stimulation or gamma knife), or treatment by transcranial magnetic stimulation (TMS). * Either of the following criteria consecutively at screening and enrollment; * Resting Pulse \> 100 bpm * Resting systolic blood pressure \> 140 mmHg, or diastolic blood pressure \> 90 mmHg * Significant dementia or a Mini-Mental State Examination (MMSE) score of ≤ 23. * Subject has a history or evidence of suicidal ideation (severity of 4 or 5) or any suicidal behavior based on an assessment with the Columbia-Suicide Severity Rating Scale (C-SSRS) at baseline. * Anyone otherwise considered unsuitable for the study by the investigator or sub-investigator including those who are unable to communicate or to cooperate with the investigator or sub-investigator.