A method of, and apparatus for, controlling the feed rate of a cutter in a machine tool of the type in which a spindle is rotated by an electric motor having operating regions of constant torque and output characteristics so as to render constant the circumferential speed of a workpiece while the workpiece is subjected concurrently to a machining operation by moving a cutter into contact therewith. The apparatus includes mechanism for computing the maximum cutter feed rate, the circumferential speed V.sub.c of the workpiece, the cutting width d of the cutter and the maximum cutting quantity Q.sub.max which is decided by the maximum power P.sub.max of the motor, mechanism for computing a spindle speed N.sub.s from the circumferential speed V.sub.c and the outer diameter D of the workpiece, mechanism for comparing the magnitudes of a base speed N.sub.b and the spindle speed N.sub.s, where the base speed N.sub.b is defined as a spindle speed at which there is a transition from the constant torque region of the motor to the constant output region thereof, and mechanism for computing the cutter feed rate f.sub.r from f.sub.r.sbsb.max,.multidot.N.sub.s and N.sub.b. The cutter is fed at the rate f.sub.r.sbsb.max when N.sub.s .gtoreq.N.sub.b and at the rate f.sub.r when N.sub.s