A spool valve is equipped with a valve body, a spool arranged in a valve chamber such that the spool can be displaced between a first position, which allows communication between an inlet port and an outlet port, and a second position, which blocks communication between the inlet port and the outlet port, a pilot valve mechanism disposed in the valve body and which causes displacement of the spool along an axial direction under the pressure of a pilot fluid that acts on one end surface of the spool, and a spring that biases the spool toward one side in the axial direction.