A circulation pressure is supplied to a starting device (2), and a working pressure that engages and disengages a lockup clutch (3) by the difference from the circulation pressure is regulated by a linear solenoid valve (10). A spool portion (121) of the linear solenoid valve (101) is provided with a first feedback oil chamber (12b) for feeding back the working pressure to a spool (12p), and a second feedback oil chamber (12a) for feeding back the circulation pressure to the spool (12p) in the direction opposite to that of the first feedback oil chamber (12p). A pressure-receiving area (A1−A2) of the first feedback oil chamber (12b) and a pressure-receiving area (A1−A2) of the second feedback oil chamber (12a) are set equal to each other in the spool (12p). Thus, an oil pressure acting force of the working pressure of the first feedback oil chamber and that of the circulation pressure of the second feedback oil chamber can be equal to each other, whereby engagement/disengagement control and slip control of the clutch can be accurately performed.