PURPOSE: To operate auxiliary machines efficiently by providing means for outputting an electric signal for switching the characteristic of a variable-speed pulley disposed between an output rotary shaft of an engine and input rotary shafts of the auxiliary machines.

CONSTITUTION: A variable-speed pulley 7 is disposed between an output rotary shaft 12 of an engine 2 and input rotary shafts 3aW6a of auxiliary machines, and adapted to switch the speed change characteristic in response to an electric signal. A control unit 69 is adapted to discriminate whether a solenoid clutch 13 of the variable-speed pulley 7 is turned on or off according to a speed signal S1, a water temperature signal S2, a field magnet signal S3, a on-off detection signal S4 of a solenoid clutch, and voltage signals Y1, Y2 showing the stepping state of an acceleration pedal. Thus, the respective auxiliary machines can be operated efficiently.