Step motor driving device

A step motor driving device comprising:

• a step motor that includes a rotor that is magnetized by two or more poles, a stator that transmits a magnetic force to the rotor and a coil that generates a magnetic force toward the stator;
• a drive circuit that outputs a measurement drive signal to the coil;
• a phase detecting circuit that detects a counter-electromotive current that occurs in the coil after the output of the measurement drive signal, and determines whether a phase of the rotor is a desired phase based on the detected counter-electromotive current;
• and
• a control unit that controls the step motor by a first driving method, in which the drive circuit outputs a first drive signal for rotating the rotor by one step, when the phase is the desired phase, and controls the step motor by a second driving method different from the first driving method so as to restrict the rotation of the rotor when the phase is not the desired phase.