Rocker Shaft

A plurality of oil passages is formed in a shaft body of a rocker shaft, which partially constitutes a valve drive system of an internal combustion engine. A bolthole is formed in the shaft body in such a manner as to substantially perpendicularly intersect the axis of the shaft body. A bush is fitted into the bolthole in such a manner as to prevent the bolthole from establishing communication between the pluralities of oil passages.