There is provided a therapeutic agent for Alzheimer's disease and Lewy body dementia for combined use of (S)-7-(2-methoxy-3,5-dimethylpyridin-4-yl)-1-(tetrahydrofuran-3-yl)-1H-pyrazolo[4,3-c]quinoline-4(5H)-one represented by formula (1):or a pharmaceutically acceptable salt thereof, and donepezil represented by formula (II):or a pharmaceutically acceptable salt thereof.