In a method of detecting synchronization loss in a stepping motor, a means for applying either control current or control voltage to a coil of each phase to thereby drive a stepping motor and a means for individually measuring a back EMF voltage induced at the coil of each phase are employed, wherein application of either the control current or the control voltage at the coil of each phase is halted by turns phase by phase for such a short time period as not to affect rotation of a rotor of the stepping motor at a predetermined timing within one step period of the rotor, the back EMF voltage at the coil is measured during the short time period, and the stepping motor is judged to lose synchronization when the measurement result of the back EMF voltage at the coil of at least one phase satisfies a detection criterion.