Abstract: The present invention provides a controller with a function of detecting status to be losing synchronism for a stepping motor driven by constant-current system. A current controller 404 applies the driving-current to a stepping motor 401 in accordance with the command derived from a control unit 407. The applied current is observed by a current measuring unit 403, and stored in a current observing unit 409 in response to the sampling signals generated from a sampling signal generating unit 408. After an excitation has completed, the observing waveform is compared with a predetermined reference waveform in the control unit, and it is determined that a loss of synchronism occurs in the stepping motor when these do not agree within a predetermined tolerance.