Abstract: This invention relates to a castor positioning device and in particular to one including a positioning shell generally conical in shape and having a hole at the top and an open end at the bottom, an actuating member formed at the center with a threaded through hole and a hexagonal contour from which extends downwardly an engaging portion having a thin stopper at the bottom end thereof and a castor having on the top a vertical screw extending upwardly through the hole of the positioning shell and then engaged with the threaded through hole of the actuating member, whereby the invention is applicable to be mounted on machines with or without transverse rods at the bottom frame thereof.