PURPOSE: To eliminate difference in the degree of vulcanization in the internal and external faces and to drastically shorten a vulcanization time by introducing a heating medium into a mandrel and heating an unvulcanized rubber hose from both the internal and external faces.

CONSTITUTION: An unvulcanized rubber hose 24 is fitted to the external circum ferential face of a mandrel 22. Manifolds 52, 54 are connected with both axial ends of the mandrel 22 via a supply pipe 38 and a discharge pipe 40 of steam. A dolly 20 is introduced into a vulcanization can 10 to the position wherein the joint holes 82 of manifolds 52, 54 are opposed to a supply pipe 60 and a discharge pipe 62. The supply pipe 60 and the discharge pipe 62 are projected from the respective evacuation positions by a cylinder 72 and joined to the joint holes 82 of the respective correspondent manifolds 52, 54. After the aper ture of a can main body 14 is closed, steam is supplied into the vulcanization can 10 through the blowout pipe 28 of steam. On the other hand, steam is passed into the mandrel 22 through the supply pipe 60, the manifold 52, the supply pipe 38 and the discharge pipe 40 of steam, the manifold 54 and the discharge pipe 62.