PURPOSE: To closely bond a resin pipe to the inner surface of a metal pipe without leaving air between both pipes when the resin pipe is thermally expanded by feeding the metal pipe in which the heat-expansible resin pipe coated with an adhesive is inserted into a heating furnace to be closely bonded to the inner surface of the metal pipe.

CONSTITUTION: An M-shaped cooling zone B is arranged on an upstream side where a metal pipe 1 in which a resin pipe is inserted is fed into a V-shaped heating furnace A. The metal pipe 1 is heated from the central part thereof to both end parts thereof within the heating furnace A but the surface temp. of the metal pipe 1 is held to 10-60°C in the cooling zone B until heating is started to prevent that the resin pipe 2 is expanded before fed into the heating furnace A.