To provide an exhaust valve hydraulic drive unit capable of controlling valve opening speed of an exhaust valve before reaching the maximum lift of the exhaust valve with high precision, and reducing driving power in the hydraulic drive unit.

In this exhaust valve hydraulic drive unit to supply working fluid to an exhaust valve actuator to drive the exhaust valve to open/close, a drive piston is composed of a two-stage diameter piston having a large diameter part and a small diameter part. It is provided with a cushion chamber parted and formed by a step part between the large diameter part and the small diameter part, and an inner surface of a drive cylinder, and a cushion oil passage and a cushion oil return passage to supply/return cushion coil in the cushion chamber.