A drug injection device includes a main body case having an injection needle let-in/let-out opening, a drug syringe mounting component that is provided inside the main body case and in which a drug syringe is mounted, a piston that is movable with respect to the drug syringe mounting component, a drive mechanism that drives the piston, a controller that is electrically connected to the drive mechanism, and an acceleration sensor that is electrically connected to the controller. This drug injection device allows the injection of a drug to be carried out safely and properly.
