To reduce the drive power consumption of a circular knitting machine by reducing the contact area of a tool for the knitting machine with the side faces of a thin groove to suppress a rise in temperature and the thermal deformation of the knitting machine by frictional heat.A part of the stem (17) of the tool for the circular knitting machine is raised from the bottom face (20) of the thin groove (19) in which the tool for the circular knitting machine is inserted and, at the same time, sunk from the upper end face (21) of the thin groove to form float parts (22, 22A to 22L) extending parallel with the thin groove (19). When a distance (L) between the bottom face and the upper end face of the thin groove (19) is used as a reference, the float part is so formed that its raised length (L1) is 10 to 40% of (L) and its sunk length (L2) is 10 to 40% of (L).