Abstract: A motor speed control system utilizing a pulse duty controlling element including a core of an amorphous, magnetically soft material having a first and a second coil disposed thereon. A first set of pulses are applied to one end of the first coil while a constant voltage or a second set of pulses are applied to one end of the second coil. A duty controlled pulse is outputted from the other end of the first coil for supply to an electric motor. The other end of the second coil is connected to a current level controlling transistor, the base of which is connected to speed presetting means. The output pulse appearing at the other end of the first coil has a rising edge which lags behind the rising edge of a pulse in the first set of pulses by a time delay which depends on the degree of conduction of the transistor which is in turn determined by a preset value of the speed presetting means, and has a falling edge which is substantially synchronized with the falling edge of the pulse in the first set.