A detent structure for a rocker shaft includes a camshaft, a rocker shaft, a shaft support, and a detent part. The camshaft is provided at a cylinder head of an engine. The shaft support is provided at the cylinder head to support the rocker shaft and has a support surface supporting the rocker shaft. The detent part is to prevent rotation of the rocker shaft. The detent part includes a bolt insertion hole and a detent bolt. The bolt insertion hole is displaced from a central axis of the rocker shaft and passes through the rocker shaft. The detent bolt is provided in the bolt insertion hole and is fastened to the shaft support to pass across the support surface.