The pharmaceutical injection device (100) comprises a syringe mounting portion (2) configured to mount thereon a syringe (9) containing a drug (12), the syringe including at a front end side thereof an injection needle mounting portion (10) on which an injection needle is mounted and a gasket (11) at a rear end side thereof, a plunger (13) operable to press the gasket (11) in the syringe (9) mounted on the syringe mounting portion (2) toward the injection needle mounting portion (10), a motor (14) operable to drive the plunger (13), an encoder (15) operable to detect a rotation amount of the motor (14), and a controller (17) connected to the encoder (15) and operable to control a driving of the motor (14). The controller (17) is operable to obtain a motor rotation amount that corresponds to a deformation amount of the gasket (11) deformed by the plunger (13), and control a rotation of the motor at a time of injection of the drug (12) in accordance with the motor rotation amount.
