To provide an energy recovery device in which pistons 8a, 8b do not collide with end faces of cylinder devices 7a, 7b in a filling process, and an impact of the collision is small even if the pistons abut on the end faces.

The two cylinder devices 7a, 7b are made to communicate with two passage switching devices 20a, 20b, respectively, and fifth and sixth position detectors 36a, 36b for detecting the movement and passage of the pistons 8a, 8b are arranged at other side ends of the two cylinder devices 7a, 7b. Passage resistance is made large in a state that a passage area between a flow-out port and a flow-in port is narrowed by the passage switching devices 20a, 20b by signals of the fifth and sixth position detectors 36a, 36b of the cylinder devices in the filling process, and the moving speed of the pistons is decelerated by applying brake actions to the pistons.