PURPOSE: To prevent lowering of the follow-up ability and increase of friction during high speed rotation by decreasing the affection upon the inertial mass by the weight of a member for coupling and discoupling adjacent rocker arms to and from each other.

CONSTITUTION: An inner rocker arm 15 is made into contact with a cam 13 so as to swing about a support shaft 16 as a center. An outer rocker arm 19 swings about support shafts 10, 11 as a center so as to open and close an intake valve 1. Inner and outer three sleeves are fitted on a rocker shaft 5 so as to be reciprocatable. Splines are formed on the respective sleeves so that they are adapted to be engaged with splines at the inner peripheral surfaces of the support shafts 10, 16, 11. The sleeves are engaged with the splines of the adjacent shafts 10, 16, 11, bridging therebetween so that they can take a coupling position where the inner and outer rocker arms 15, 19 are coupled with each other and a discoupling position where the rocker arms 15, 19 are discoupled from each other.