To periodically change over the operating direction of a hydraulic actuator by a hydraulic pressure by providing a main spool and a pilot spool which change over 5 the position of the main spool by the hydraulic pressure generated by interlocked therewith.

When a changeover valve 6 becomes in an operating position A, the pressure of a high-pressure passage 28 is reduced to be lead in a pilot spool pressure chamber 22 and a main spool pressure chamber 21, the pressure in a low-pressure passage 29 is led to a pilot spool pressure chamber 12 and a main spool pressure chamber 11, a pilot spool 5 is held in a contracted position, and the main spool 4 is moved in the contraction direction. Along with it, the pressure of the pilot spool drive pressure chamber 13 increases to change over the pilot spool 5 in a extended position so that the main spool 4 starts to move in the extension direction. A piston 80 which is in a contracted position till a neutral position moves in the contraction direction and after passing over it, it is changed over to the extension direction, and the piston 80 moves in the extension direction.