PURPOSE: To improve the extent of resoponsiveness in a governor unit by smoothing the relative vertical motion of a rack pin.

CONSTITUTION: A rack pin 6 of a fuel injection pump is engaged with an engaging groove 11 of a fork lever 1, and thereby this rack pin 6 is constituted so as to be moved for metering by tension of a governor spring acting on the fork lever 1 and force of a governor G. The pin engaging groove 11 of the fork lever 1 is formed into a cycloid curve in which a contact angle α between the pin engaging groove 11 and the rack pin 6 becomes constant even if a rocking angle θ of the fork lever 1 is varied to some extent.