An engine valve operating system is provided in which a rocker arm that swings by following a valve operating cam abuts against an engine valve via a hydraulic tappet, a receiving member (41) receiving the hydraulic tappet (12) being slidably fitted into the rocker arm (13), the hydraulic tappet (12) being fitted into the rocker arm (13), a restricting part (29) being provided so as to face the receiving member (41) from the side opposite to the hydraulic tappet (12), and an adjustment screw (44) for adjusting a clearance between the restricting part (29) and the receiving member (41) when the engine valve is in a valve-closed state being screwed into an engine main body (5) so that its position can be adjusted back-and-forth so as to abut against the receiving member (41) when the engine valve is closed. This enables the amount of lift of the engine valve to easily be adjusted with good precision while eliminating the need for complicated machining or production control when opening or closing the engine valve via the hydraulic tappet by means of the rocker arm.