To remarkably improve the operability so as to smoothly control the revolution speed of a prime mover by detecting the turning displacement of a turning mechanism to be displaced in response to the operated variable of a direct acting lever and a foot-operated pedal with a potentiometer.

A turning mechanism 19 is formed of a lever side rotor 20 connected to a direct acting lever 14, a pedal side rotor 26 connected to a foot-operated pedal 15, and a displacement transmission unit 36 for transmitting the turning displacement from the lever side rotor 20 to the pedal side rotor 26. When the direct acting lever 14 is tilted for operation, the lever side rotor 20 is turned for displacement, and this displacement is transmitted to the pedal side rotor 26 through a displacement transmission unit 36. The pedal side rotor 26 is thereby turned so as to turn a detecting lever 37A of a potentiometer 37 through a link 38. When the foot-operated pedal 15 is operated, the only pedal side rotor 26 is turned for displacement, and the detecting lever 37A is turned.