Depression is common in Parkinson's disease (PD), but the effective treatment is not established yet. tDCS is a non-invasive brain stimulation to modulate brain function. The tDCS on the depression in general population were already conducted, but not in PD. This study is to know whether transcranial direct current stimulation (tDCS) is effective for the treatment of depression in PD. Participant will be asked to visit three consecutive days for the non-invasive stimulation.

Inclusion Criteria:

• UK Parkinson's disease brain bank criteria
• more than 19 years old
• Able to provide consent for the protocol
• Depression (based on DSM-IV criteria)

Exclusion Criteria:

• Dementia
• Unpredictable symptom fluctuations
• Contraindication to tDCS (i) irritations, cuts, lesions in the brain (ii) any preexisting unstable medical conditions, or conditions that may increase the risk of stimulation such as uncontrolled epilepsy (iii) history of severe cranial trauma with alteration of the cranial anatomy or metallic intracranial implants (iv) history of seizure
• Subjects without the capacity to give informed consent
• If participation in the study would, in the opinion of the investigators, cause undue risk or stress for reasons such as excessive fatigue, general frailty, or excessive apprehension