PURPOSE: To form corrugations efficiently on the barrel part of a cylindrical container by putting a cylindrically formed container between a cylindrical shape-retaining jig with a corrugated shape and a cylindrical mold with a corrugated shape and revolving said jig and mold heating said container.

CONSTITUTION: A formed cylindrical container 1 is inserted into a cylindrical shape-retaining jig 6 with a circular corrugated shape and the jig is brought approximately into close contact with the inside of the barrel part 2 of the cylindrical container 1. Hot water (60°C) is poured from a water supply pipe 9 built in this jig 6 and circulated. Further, the barrel part 2 of the cylindrical container 1 into which the shape-retaining jig is inserted is inserted into a mold 10 having a corrugated part 7 on the inner circumferential surface. The mold 10 is heated by a heater 12 from outside, the mold 10 and the shape-retaining jig 6 are revolved in the same direction and the barrel part 2 of the cylindrical container 1 is pinched by the corrugated parts 11, 7 to form a corrugated part 5. A corrugation can be formed securely with a comparatively simple device.