Abstract: A motor driver for driving a motor in a valve timing controller of an internal combustion engine, including an Electronic Driver Unit (EDU) that, upon receiving a target rotation cycle as the instructed rotation cycle, instructs a rotation controller to (i) calculate a duty value of a Pulse Width Modulation (PWM) signal for driving the motor based on an instructed rotation cycle and an actual rotation cycle and (ii) output a calculation result of the duty value to a motor drive unit, with the rotation controller outputting, to the motor drive unit, an instruction signal that rotates the motor forward along an actual rotation direction, when the calculation result takes a positive value as a duty ratio of the PWM signal, establishing an accurate motor rotation speed control together with an improved responsiveness.