Depression, apathy, and anhedonia are often comorbid in patients with Parkinson's disease. Since the morbid states of apathy and anhedonia are complicated, these symptoms are often difficult to diagnose. Several therapeutic methods for apathy and anhedonia are considered effective. However, the validity of these methods has not been established. Similar to depression, apathy and anhedonia clearly affect the quality of life of patients and their families. Therefore, accurate diagnoses of morbid states in the early stage of the disease and corresponding appropriate treatments should be given high priority.