This pharmaceutical injection device comprises a main body case (2); a pharmaceutical syringe mounting portion (3) provided inside the main body case (2); a piston (5) that is provided so as to be movable with respect to a pharmaceutical syringe (4) that is removably attached to the pharmaceutical syringe mounting portion (3); a drive mechanism (6) for driving the piston (5); a controller (7) that is electrically connected to the drive mechanism (6); and an acceleration sensor (8) that is connected to the controller (7). When a manual mixing mode of the pharmaceutical syringe (4) is selected, the controller (7) changes to the next step (air venting mode) if the inclination angle of the main body case (2) sensed by the acceleration sensor (8) is greater than a specific value.
