A spool valve comprising: a first housing including passages (22, 23, 24) and a slide hole; a spool slidably located in the slide hole; a second housing that forms a servo chamber that is coaxial with the slide hole; a sleeve slidably located in the servo chamber, the sleeve dividing the servo chamber into a first pressure chamber and a second pressure chamber, the first pressure chamber being adjacent to the first housing, the second pressure chamber being away from the first housing; a piston slidably fitted in the sleeve and extending from inside the sleeve beyond the second pressure chamber; a nut; a screw shaft screwed with the nut; and an electric motor that rotates the screw shaft, wherein the second housing includes a drain port and an input port that is to be connected to a pressure source of a hydraulic fluid, the first pressure chamber communicates with the input port, in a balanced state where a force that is applied to the sleeve by the hydraulic fluid in the first pressure chamber, and a force that is applied to the sleeve by the hydraulic fluid in the second pressure chamber, are balanced, the second pressure chamber is blocked from the input port and the drain port by the piston, from the balanced state, when the piston shifts in a direction toward the spool, the second pressure chamber comes into communication with the input port, and from the balanced state, when the piston shifts in a direction away from the spool, the second pressure chamber comes into communication with the drain port; characterised by the sleeve being coupled to the spool in the first pressure chamber, and the nut being fixed to the piston. a first housing including passages (22, 23, 24) and a slide hole; a spool slidably located in the slide hole; a second housing that forms a servo chamber that is coaxial with the slide hole; a sleeve slidably located in the servo chamber, the sleeve dividing the servo chamber into a first pressure chamber and a second pressure chamber, the first pressure chamber being adjacent to the first housing, the second pressure chamber being away from the first housing; a piston slidably fitted in the sleeve and extending from inside the sleeve beyond the second pressure chamber; a nut; a screw shaft screwed with the nut; and an electric motor that rotates the screw shaft, wherein the second housing includes a drain port and an input port that is to be connected to a pressure source of a hydraulic fluid, the first pressure chamber communicates with the input port, in a balanced state where a force that is applied to the sleeve by the hydraulic fluid in the first pressure chamber, and a force that is applied to the sleeve by the hydraulic fluid in the second pressure chamber, are balanced, the second pressure chamber is blocked from the input port and the drain port by the piston, from the balanced state, when the piston shifts in a direction toward the spool, the second pressure chamber comes into communication with the input port, and from the balanced state, when the piston shifts in a direction away from the spool, the second pressure chamber comes into communication with the drain port; characterised by the sleeve being coupled to the spool in the first pressure chamber, and the nut being fixed to the piston.