In a switching valve containing a valve member for opening and closing a valve seat and a piston for driving the valve member by the action of a pilot fluid pressure inside a valve housing, a magnet for positional detection is attached to the piston, two sensor attachment grooves extending in the direction of the axial line L of the switching valve and having different groove lengths in accordance with the operational position are formed in parallel on the side face of the valve housing, and magnetic sensors are attached at locations on the side of the innermost end wall in the attachment grooves.