A rocker arm is tilted by a cam so as to open and close a valve provided on a cylinder head. This arm comprises a pair of opposing wall portions which are made by folding a flat plate so that they oppose substantially in parallel and cylindrical expanding portions which are formed at tilting fulcrum shaft mounting portions located in a center of the opposing wall portions in the length direction thereof, the expanding portions being expanded in the direction of the tilting fulcrum shaft. The cylindrical expanding portions which are thicker than the opposing wall portions receive a load accompanied by the tilting motion so as to decrease bearing stress applied to the opposing wall portions.