The present invention provides a novel compound having an excellent acetylcholinesterase inhibitory effect. That is, it provides a 4-substituted piperidine compound fluoride represented by the following formula, a pharmaceutically acceptable salt thereof or hydrates thereof (provided that 1-benzyl-4-[(5,6-dimethoxy-2-fluoro-1-indanon)-2-yl]methylpiperidine, a pharmaceutically acceptable salt thereof and hydrates thereof are excluded).
wherein R1 and R2 represent substituents.