To drive an electric motor stably and highly reliably, even if the waveforms of an induced voltage of the motor are distorted.

This electric motor driving device is provided with: an induced voltage presuming part 13 that presumes the induced voltage from current and output voltage values of the motor; a rotor position and speed detecting part 14 that presumes the magnetic pole position of a rotor based on the induced voltage value presumed; and an induced voltage correcting part 12 that filters the induced voltage value by a specified process to stabilize the presumption. This structure enables the motor to be driven stably, no matter what kind of the waveforms the induced voltage of the motor has. Also, this device is provided with a driving abnormality detecting part 15 that judges a driving abnormality in accordance with the induced voltage value presumed. Thus, if a driving abnormality occurs, it is detected and an immediate abnormality removing process is executed to drive the motor highly reliably.