Piston valve and lubricating oil supply device

A drain port 82d of LUBE relay valve 80 as a spool valve is tapering portion 83b formed with a, 82c of the gradually tapered toward a discharge port. Consequently, foreign substances that adhere to the peripheral edge of the drain port 82d to the distal end of the tapered portion 83b to be moved when a piston plug 84 remains with the edge of a web 84a of the piston 84, which is caught by such foreign substances. As a result, the discharge port may 82d only through a gap at the distal end portion of the tapered portion to be 83b open when the piston plug 84 remains, and thus it is possible to provide a sufficient flow rate of the dispensed lubricant oil from the output terminal 82c in a mode with normal lubrication sure.