A driver comprises a direction-switching means which switches a rotation direction of a rotary driving source based on a direction instruction signal, a current amplifier/limiter which converts a voltage outputted from the direction-switching means into a corresponding current and which limits the current to a preset reference current I.sub.MAX (threshold value), a current sensor which detects the current supplied to the rotary driving source, and a current loop which feeds back a detection signal supplied from the current sensor to an upstream side of the current amplifier/limiter.