PURPOSE: To produce a compound tube efficiently through press fit of an inner tube into an outer tube by admitting compressed gas into a space with the inner tube housed in a long thin closed space while the outer tube arranged at one end of the space communicated thereto.

CONSTITUTION: An outer tube 2 is mounted to mount section 45 of an outer tube fitting 13 which has been removed from a housing 11 while an inner tube 1 is housed at a long thin space 11 in the housing 11. The fitting 13 is screwed on the housing 11. Then, a normally closed solenoid valve 23 is opened to allow a lubricating liquid to be introduced into the space 31 from a tank 21. After that, the valve 23 is closed while a normally closed solenoid valve 15 is opened to allow high pressure compressed gas to be introduced into the space 31 from supply source 17. The lubricating liquid passes through a tapered guide path 42, a central path 41, an axial port of a tube 2 and then drained, while the tube 1 is force-pressed into the tube 2 by the lubricating liquid through the guide path and the path 41.