Valve operating system in internal combustion engine

A valve operating system includes a connection switch-over device (381;382) provided in a plurality of cam followers (191,201;192,202,21). The connection switch-over device has a piston (39) moved in response to a change in hydraulic pressure in a hydraulic pressure chamber (431;432). A roller shaft (331;62,65) is disposed on at least one of the cam followers and has a roller (281;282,61) carried thereon to come into rolling contact with a valve operating cam (26). In this valve operating system, the hydraulic pressure chamber and a communication passage (481;482), which permits an oil supply passage (44) to communicate with the hydraulic pressure chamber, are defined in a particular one (191;192) of the cam followers, which moves a smallest amount when the connection switch-over device is in its disconnecting state. The roller shaft, having the roller rotatably carried thereon, is mounted on the cam follower (201;202,21) other than the particular one cam follower. Thus, it is possible to avoid an increase in size of the particular one cam follower, and avoid a complicated assembling operation and passage construction. Moreover, the valve operating load is reduced to a minimum by using the roller.