There is provided a therapeutic agent for Alzheimer's disease and Lewy body dementia for combined use of (S)--(2-methoxy-3,5-dirnethylpyndin-4-y1)-1-(te ahydrofuran-3-y1)-1H-pyrazolo[4,3-c]qui 5 noline-4(51-1)-one represented by formula (I): O or a pharmaceutically acceptable salt thereof, and donepezil represented by formula (II): 0 0 0 or a pharmaceutically acceptable salt thereof 20