A regulator valve is structured such that hydraulic pressure to be output from a regulated pressure output port is regulated according to urging forces, i.e., line pressure to be regulated, throttle pressure, spring force from a compression coil spring, and operating force from a plunger, which are applied to a valve spool. The plunger has a small diameter portion and a large diameter portion having a diameter larger than the diameter of the small diameter portion, both of which are axially displaceably retained in a spring receiving sleeve. The small diameter portion is urged in one axial direction at one end of the plunger that protrudes into a spring chamber and faces the valve spool, while the large diameter portion is urged in the other axial direction by range pressure at the other end of the plunger which is isolated from the small diameter portion located in the spring chamber.