A retired 84-year-old male presented with depression, lack of energy, anhedonia, social withdrawal, poor sleep, poor memory, and cognitive impairment after the death of his wife. An antidepressant agent was administered after the provisional diagnosis of the first episode of major depressive disorder with pseudodementia. However, symptoms such as impaired cognitive function, poor memory, and impaired life function persisted after adequate antidepressant doses. The diagnosis was revised to dementia with depression because of the pattern of symptoms and signs, clinical response, and past history. Under the corrective diagnosis, he received appropriate treatment.