An endoscope has a channel switching device for use in switching over a suction channel. The channel switching device consists broadly of a cylinder unit and valve unit. The valve unit can be disassembled into three component parts; a button assembly, piston assembly, and mount assembly. The button assembly has a cap, which is made of a rigid resin such as polyether ketone (PEEK) or polysulfone (PSU), as the uppermost part thereof. Since the cap is made of a rigid resin durable to autoclaving; such as, PSU or PEEK, the valve unit will not be damaged due to autoclaving. Even when the autoclaved valve unit is put to use though it is not yet cooled down, an operator will not perceive heat very much but can manipulate the endoscope as he/she intends.