The pharmaceutical injection device of the present invention comprises a cartridge holder, a main case, a piston, a motor, an opening component, an open/closed detection switch, and a controller. The motor drives the piston in either an insertion direction in which the piston is inserted into a pharmaceutical cartridge, or a pull-out direction in which the piston is pulled out of the pharmaceutical cartridge. The opening component opens the cartridge holder in conjunction with the movement of the piston in the pull-out direction. The open/closed detection switch detects whether the cartridge holder is open or closed. When the open/closed detection switch detects that the cartridge holder is open, the controller controls the motor so as to stop the piston.