A lost motion mechanism that biases a free rocker arm of a lift-amount changing member capable of lifting a valve in a direction to abut against a cam includes a spring accommodated in a support portion. The support portion is a recessed portion integrally formed on a camshaft holder below the free rocker arm. The vertical dimension of an engine is reduced as compared with a case where the support portion is provided above the free rocker arm. A camshaft cap supports the camshaft and a bolt that fastens the camshaft cap to the camshaft holder are not required.