An apparatus for correcting the circumferential length of a metal ring has a drive roller 2 and a driven roller 3 positionable closely to each other for training a metal ring W therearound, and a correcting roller 4 disposed between the drive roller 2 and the driven roller 3. The apparatus also has a first displacement applying unit for displacing the drive roller 2 and the driven roller 3 away from each other when the metal ring W is trained around the drive roller 2, the driven roller 3, and the correcting roller 4. The apparatus further includes spacers 21, 22 for spacing the drive roller 2 and the driven roller 3 a predetermined distance from each other when the drive roller 2 and the driven roller 3 are released from being displaced, a second displacement applying unit 27 for displacing the correcting roller 4 in a direction perpendicular to the direction in which the drive roller 2 and the driven roller 3 are displaced and also to extend the metal ring W, thereby to correct the circumferential length of the metal ring W, and a third displacement applying unit 91 for displacing the drive roller 2 and the driven roller 3 toward each other when the drive roller 2, the driven roller 3, and the correcting roller 4 are released from being displaced by the first and second displacement applying units 10, 27.