PURPOSE: To control the speed change of a DC motor with a simple circuit configuration by controlling to feed a current of a motor main circuit on the basis of a comparison output of a voltage proportional to the operating stroke of an operating lever with a reference triangular wave.

CONSTITUTION: The output of a triangular wave oscillator 82 is connected with one input terminal of a comparator 83, and a variable reference voltage generator 84 is connected with the other input terminal of the comparator 83. The generator 84 outputs a voltage proportional to the operating stroke of an operating lever. The comparator 83 compares a pulse width control signal (a) from the oscillator 82 with a rotating speed set signal (b) from the generator 84, and outputs a speed change control signal. A speed change controller 85 controls to feed the current of a motor main circuit 86 through a power transistor 14 on the basis of the speed change control signal from the comparator 83.