PURPOSE: To perform an expanded tube forming of a heat recoverable resin pipe almost continuously by providing a vacuum tank with a pressurizing function while a half-split contact is used at both ends of a vacuum container.

CONSTITUTION: An inner tube 6 bored on the circumference thereof is arranged on a concentric circle with an outer tube 5 through a spacer 3 and half-split contact plug 2 are mounted at both ends of the outer tube 5. A vacuum exhaust port 7 is provided on the circumference of the outer tube 5 and connected to a vacuum pump 10 through a solenoid valve 9' and to a pressure tank 11 through a solenoid valve 9. A heat recoverable resin pipe 1 heated beyond the softening point thereof is inserted and reduced to a low vacuum to be expanded diametrically. After the expansion of tube attains the inner surface of the inner tube, the solenoid valve 9' is closed and the solenoid valve 9 is opened to peel the tube off the inner surface of the inner tube by a pressure gas.