PURPOSE: To adjust the engine speed accurately and responsively by disposing a cam pulley and an oscillating member such that a can shaft and an oscillating shaft are on the coaxial line at the cam pulley fit at the cam shaft in the engine with its rotor being an overhead cam shaft type.

CONSTITUTION: A governor arm 14 is provided at the oscillating shaft 3 of an oscillating member 4, the rotating member 15 mounted with a governor spring 6 in the outer surroundings of the oscillating shaft through a fixing side frame 18 is provided, and the one end of the spring 6 is made to be engaged with the arm 14. The other end of the spring 6 is made to be engaged with the fixing side, and the arm 14 rotates the member 15 by the torque transmitted through the spring 6. Accordingly, a throttle shaft is rotated through, for example, a link mechanism by drawing a control wire 16 provided at the member 15 so as to adjust the aperture of the throttle valve. A magnetic path is formed by fitting a magnetic member 19 facing to a permanent magnet 5 by inserting a cam pulley 2 at the frame 18 comprising magnetic materials.