A spool valve comprising: a valve body having a spool insertion hole inside of the valve body, and formed with an input port, an output port, and a drain port which communicate with the spool insertion hole; a spool slidably inserted in the spool insertion hole, and configured to selectively allow and prohibit communication between the input port, the output port, and the drain port by moving in an axial direction; an electric motor configured to drive the spool in the axial direction; a ball-screw configured to convert a rotary motion of the electric motor to a linear motion of the spool in the axial direction such that when the electric motor is rotated in one direction, the spool is moved to a first position where the spool allows communication between the input port and the output port, while shutting off communication between the output port and the drain port, and when the electric motor is rotated in another direction, the spool is moved to a second position where the spool shuts off communication between the input port and the output port, while allowing communication between the output port and the drain port; characterised in that said spool valve further comprises an elastic member biasing the spool toward the second position and such that the spool and the linear motion member of the ball-screw are rotationally fixed in position by said elastic member; wherein said elastic member comprises a compression coil spring having a first bent piece at one end of the compression coil spring, and a second bent piece at another end of the compression coil spring, wherein the first bent piece extends in the axial direction and is slidably inserted in an axial hole formed in an end surface of the spool, and the second bent piece is in engagement with the valve body. a valve body having a spool insertion hole inside of the valve body, and formed with an input port, an output port, and a drain port which communicate with the spool insertion hole; a spool slidably inserted in the spool insertion hole, and configured to selectively allow and prohibit communication between the input port, the output port, and the drain port by moving in an axial direction; an electric motor configured to drive the spool in the axial direction; a ball-screw configured to convert a rotary motion of the electric motor to a linear motion of the spool in the axial direction such that when the electric motor is rotated in one direction, the spool is moved to a first position where the spool allows communication between the input port and the output port, while shutting off communication between the output port and the drain port, and when the electric motor is rotated in another direction, the spool is moved to a second position where the spool shuts off communication between the input port and the output port, while allowing communication between the output port and the drain port; characterised in that said spool valve further comprises an elastic member biasing the spool toward the second position and such that the spool and the linear motion member of the ball-screw are rotationally fixed in position by said elastic member; wherein said elastic member comprises a compression coil spring having a first bent piece at one end of the compression coil spring, and a second bent piece at another end of the compression coil spring, wherein the first bent piece extends in the axial direction and is slidably inserted in an axial hole formed in an end surface of the spool, and the second bent piece is in engagement with the valve body.