To provide a peripheral length correction method capable of easily and reliably correcting the peripheral length of a metal ring to a desired value and improving a yield.

A metal ring W is hung over a drive roller 2, a driven roller 3 and a correction roller 4. The drive roller 2 and the driven roller 3 are held at a prescribed interval. The correction roller 4 is displaced by a prescribed displacement quantity with respect to the reference value of the peripheral length of a metal ring W in the direction orthogonal to the displacing direction of the drive roller 2/driven roller 3 and in the direction elongating the metal ring W to correct the peripheral length of the metal ring W. An actual length of the metal ring W is measured in the state that the ring W is tensed by the rollers 2, 3. By comparing the actual length and the reference value of the length of the ring W, the difference between both is obtained. Corresponding to the difference between the actual length and the reference value, the displacement quantity of the correction roller 4 is corrected. The correction roller 4 maintains the corrected displacement quantity for a prescribed time.