The present invention includes a rocker arm 16, which has an arm roller 18 at the center, a lash adjuster 30 for supporting a fulcrum P of the rocker arm 16, an oscillation arm 20, which has an oscillation cam surface (a non-pushing section 24 and a pushing section 26) that is in contact with the arm roller 18, and an adjustment mechanism for changing the reference arm rotation angle of the oscillation arm 20 in relation to the rocker arm 16 with a view toward changing the operating angle and lift amount of a valve disc 12 within a predetermined adjustment range. The adjustment mechanism includes a control shaft 22, a roller contact surface 32, a control arm 34, and an oscillation roller arm 38. The lash adjuster 30 is positioned so that its expansion/contraction direction is substantially parallel to a virtual straight line joining the rotation center Q of the oscillation arm 20 to the rotation center S of the arm roller 18.