PURPOSE: To secure the safety of operation by quickening the response of an actual driving speed to the operation of an operation means.

CONSTITUTION: An electromagnetic proportional valve output current arithmetic part 32 calculates an output current Ia for feedback control on the basis of the deviation ΔV between the speed command signal Vc from a potentiometer 22 detecting the manipulated variable of a grip and the detection signal Vs from a speed detector 28 detecting the rotating speed of a winding drum 16. A current limiter circuit 38 reads a limit current Ir corresponding to an engine rotating speed Re out of a limiter table 34, outputs a current I less than the limit current Ir to an electromagnetic proportional value 26 at all times, and controls the degree of coupling between an engine 10 and the winding drum 16 by a modulation clutch 20.