To provide an oil pressure mechanism for power hydraulic tool capable of miniaturizing an electric motor for rotating the release cam 8 by alleviating increase in travelling stroke of a valve rod 7a when an oil pressure release valve 7 requiring the maximum torque for rotation drive of a release cam 8 starts opening and of shortening work time by reducing speed reduction ratio of rotation drive by the electric motor.

In the oil pressure mechanism for power hydraulic tool, a valve rod 7a reciprocally moves during one full rotation of a release cam 8 by being driven by a releasing electric motor, whereby an oil pressure release valve 7 returns to the closed state again through a opened state from a closed state and oil pressure of a cylinder 3 is released during the opened state of the oil pressure release valve 7. The release cam 8 employed for this configuration has a cam shape in which a moving stroke of the valve rod 7a at respective rotation angles θ from the closed state to a half rotation is always made smaller than that of the valve rod 7a at the same rotation angles θ from the closed state of the oil pressure release valve 7 in the case of employing a disc eccentric cam 6.