A cam shaft assembly is provided which includes a rolling bearing providing for effective oil feeding to a raceway. The assembly includes: a shaft 1; the rolling bearings 3 rotatably supporting the shaft 1; and cams 2 fitted on the shaft 1. The rolling bearing 3 includes a circumferential groove formed on an outer periphery of an outer ring 5 and an axial groove extending from place in the circumferential groove and opening on a lateral side of the outer ring 5.