A rocker arm 13 is rocked with respect to a control shaft 32 through a link arm 14 by rotation of a drive shaft 3. With this configuration, a rocking cam 7 is rocked with respect to the drive shaft 3 through a link member 15. A valve lifter 6 is pushed downward by rocking of the rocking cam 7. The control shaft 32 is integrally provided with a control cam which is eccentric with respect to an axis of the control shaft 32. If the control cam is rotated, a rocking fulcrum position of the rocker arm 13 is changed, thereby varying a valve-lift amount. An eccentric bush 22 is provided on an inner peripheral surface of the rocker arm 13 on an outer periphery side of the control cam. The eccentric bush 22 meshes with an inner peripheral gear formed on an inner periphery of the rocker arm 13 by an outer peripheral gear 39b, and is coupled to the rocker arm 13. This coupled state is released by moving the eccentric bush 22 in the axial direction. In this state, the eccentric bush 22 is rotated by a predetermined amount with respect to the control cam and the rocker arm 13, thereby adjusting the valve-lift amount.