Recent studies suggest that an attention deficit occurs at early stage of Alzheimer's disease and affects patients' activities of daily living. In other words, some patients without language or visuospatial dysfunction have severe impairment of activities of daily living, which might result from attention deficit. Another recent clinical study showed that galantamine is more effective in attention and vigilance of Alzheimer's disease patients than donepezil. The study hypothesis is that galantamine will improve attention and frontal executive function in Alzheimer's disease patients and is well-tolerated. 8 mg/day for the first 4 weeks, 16 mg for the next 8 weeks