PURPOSE: To easily secure oil pressure of a hydraulic rush adjuster by providing a first oil passage for connecting a chain tensioner to the bearing part of a cam shaft and a second oil passage for connecting the chain tensioner to the idler bush part of an idler shaft.

CONSTITUTION: Lubricating oil which flows in a main oil passage 40 is supplied through a third oil passage 62 to each hydraulic rush adjuster 60 and supplied through a fourth oil passage 64 to a cam chain tensioner adjuster 36. In the adjuster 36, a plunger is slid by pressurized oil to move a pressing part 50 forward and backward, and the pressing force applied to a cam chain is changed to give proper tension. Surplus oil in the adjuster 36 is discharged in such a manner as to direct the fitting surface of the adjuster 36. Some of oil supplied to the adjuster 36 is supplied to a bearing 42 part of each cam shaft through oil passages 44, 66, 68, and supplied to a bush 46 part of an island shaft 28 through an oil passage 48.