A first one-way valve is provided in a first advance passage connecting a hydraulic pump to a control advance chamber. A second one-way valve is provided in a first retard passage connecting the hydraulic pump to a control retard chamber. A first control valve is provided in a second advance passage to bypass the first one-way valve for communication of the first advance passage. A second control valve is provided in a second retard passage to bypass the second one-way valve for communication of the first retard passage. The first control valve operates by the pilot pressure to close the second advance passage at advance controlling and opening it at retard controlling. The second control valve operates by the pilot pressure to close the second retard passage at retard controlling and open it at advance controlling.