A circumferential length correcting method for a metal ring including: a circumferential length measuring step of passing the metal ring around a driving roller and a driven roller, displacing the driving roller and the driven roller away from each other, and measuring the actual circumferential length of the ring under tension; and a circumferential length correcting step of correcting the circumferential length of the ring by displacing a circumferential length correcting roller by a predetermined distance in a direction in which the metal ring is extended. The method is capable of imparting an appropriate arc shape to the metal ring while correcting the circumferential length to fall within an appropriate value range. Before the circumferential length correcting step, the method includes an arc-shape imparting step of displacing an arc-shape imparting roller, which has an arc-shaped circumference and is positioned inside a metal ring, by a predetermined distance in a direction in which the metal ring is extended, thereby imparting an arc shape conforming to the shape of the circumference of the arc-shape imparting roller to the metal ring.