The purpose of this study is to confirm the efficacy of Aricept in patients with dementia with Lewy bodies (DLB).

Inclusion Criteria

1. Patients diagnosed with probable DLB according to the diagnostic criteria for DLB
2. Patients having caregivers throughout the study who submit written consent to cooperate with this study, can routinely stay with patients at least 3 days a week (at least 4 hours a day), provide patients' information necessary for this study, assist treatment compliance, and escort the patients on required visits to study institution
3. Clinical Dementia Rating (CDR) score is greater than or equal to 0.5
4. Mini-Mental State Examination (MMSE) score is greater than or equal to 10 and less than or equal to 26

Exclusion Criteria

1. Patients diagnosed with Parkinson's disease with dementia (PDD)
2. Patients who have received anti-dementia drug therapy within 12 weeks before the start of the observation period
3. Patients with a complication of serious neuropsychiatric disease(s) such as stroke, brain tumor, schizophrenia, epilepsy, normal pressure hydrocephalus, mental retardation, brain trauma with unconsciousness, or a history of brain surgery causing unrecovered deficiency
4. Patients with severe extrapyramidal disorders (Hoehn and Yahr staging score is greater than or equal to IV)
5. Patients whose systolic blood pressure is less than 90 mmHg or pulse rate is less than 50 beats/minute at screening test