Depression is a common symptom in Parkinson's disease (PD) and its frequency is about 40%. But, frequency of major depression in PD is about 2.2-7.7% and similar to age-matched aged group. Depressive state (depression), not major depression, is an essential feature of PD derived from impairment of mesocortico-frontal dopaminergic pathway. But, PD has many impaired neurotransmitter systems including dopamine, serotonin and noradrenaline. As a neurochemical background is complicated, we have not yet drugs for depression in PD.