Transcranial Direct Current Stimulation for Depression in Alzheimer's Disease Patient - Preliminary Research

Inclusion Criteria: 1. Participants who meets criteria of probable Alzheimer's disease defined by NINCDS-ADRDA research criteria. 2. Participants who meets criteria of depression in Alzheimers defined by NIMH criteria. 3. Participants who have been on fixed dose (including participants without any prescription) of antidepressants for at least two weeks on the screening visit. 4. Participants who have been on fixed dose (including participants not prescribed) of antidementia drugs (donepezil, rivastigmine, galantamine, and memantine) for at least for weeks on the screening visit. 5. Ambulatory participants with or without any aiding device 6. Participants who have one caregiver, who must live with the patient at least ten hours a week and must report the patient's behavior. 7. A study partner who can report how the participant is doing is needed. 8. Eligible family member must sign and give consent on behalf of participants, whereas participants can give assent. Exclusion Criteria: Following potential participants will be excluded 1. In case their cognitive deficits are better explained by another disease (e.g., cerebral infarction, Parkinson disease, multiple sclerosis, normotensive hydrocephalus). 2. In case they have history of epilepsy 3. In case they need treatment by antipsychotics due to significant psychotic symptoms 4. In case they have urgent risk of suicide or severe depression and any doctor require their hospitalization to psychiatric units. 5. In case they have history of ineffectiveness with electroconvulsive therapy (ECT) or transcranial direct current stimulation (tDCS) 6. In case ECT or tDCS is clinically contraindicated 7. In case they are taking benzodiazepines or antiepileptic drugs on the screening visit 8. In case they scored less than ten on Mini Mental State Exam (MMSE) or scored 3 or more on Clinical Dementia Rating (CDR) 9. In case his/her GDS score is lower than 6 at baseline 10. In case he/she is unable to agree video recording on evaluation interview