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