PURPOSE: To reduce variations in revolution of the drive mechanism of a distributor to prevent component parts from being broken, by providing an intermediate gear for driving the distributer in addition to a cam gear for driving a cam shaft, and by meshing the cam shaft and the intermediate gears with a timing belt.

CONSTITUTION: A timing belt 1 drives a cam gear 21 in a cam drive system 2, and the cam gear 21 is fixed to a cam shaft 22 with bolts 23, and meshes with an intermediate gear 61 to drive a distributor driven gear 7 in a distributor through a drive shaft 64 and a drive gear 68. Thus, variations in revolution of the distributor drive system may be reduced to prevent the ignition timing from shifting, thereby it is possible to prevent component parts from being broken.