A motor driving device manufacturing method for manufacturing a motor driving device including a motor case, a rotor, and a stator disposed concentrically with the rotor on the outer periphery of the rotor, includes a measuring step for measuring a position of the stator relative to an axial center of the rotor from an inner side of the stator using a measuring device inserted in the stator; an adjusting step for adjusting the position of the stator from the inner side of the stator based on a measurement result of the measuring step using an adjustment device inserted in the stator, wherein the measuring step and the adjusting step are executed in a rotor not-inserted state, in which the stator is housed in the motor case and the rotor is not inserted in the stator; a stator fixing step for fixing the stator in the motor case; and a rotor shaft-support step for inserting the rotor in the stator and shaft-supporting the rotor on the motor case.