To easily produce a hollow member while reducing production cost.

A core 14 is formed into a cylindrical shape having an expanded part 14A longitudinally provided to the central part thereof by using polyacetal as a material and a mold 16 is loaded with the core 14. By injecting nylon into a cavity 18 from an injection port 20 in the state loaded with the core 14, nylon is charged on the outer peripheral side of the core 14 within the cavity 18 to mold a hollow member. Thereafter, the hollow member integrally taken out of the mold 16 along with the core 14 is heated to temp. lower than the m.p. of nylon but capable of gasifying polyacetal and the material of the gasified core 14 is discharged out of the hollow member.