The present invention relates to a pharmaceutical injection device, and it is an object thereof to make this device easier to use, such as by opening a cartridge holder automatically. In order to achieve this object, the pharmaceutical injection device of the present invention comprises a cartridge holder (7), a main case (1), a piston (10), a motor (13), an opening component (130), an open/closed detection switch (24), and a controller (25). The motor (13) drives the piston (10) in either an insertion direction (C) in which the piston (10) is inserted into a pharmaceutical cartridge (9), or a pull-out direction (D) in which the piston (10) is pulled out of the pharmaceutical cartridge (9). The opening component (130) opens the cartridge holder (7) in conjunction with the movement of the piston (10) in the pull-out direction (D). The open/closed detection switch (24) detects whether the cartridge holder (7) is open or closed. When the open/closed detection switch (24) detects that the cartridge holder (7) is open, the controller (25) controls the motor (13) so as to stop the piston (10).
