To provide a method of producing a double pipe by which the double pipe can be produced even in a tube stock thinner in wall thickness.

The tube stock 1 is inserted into a tapered hole of a clamp die and a punch is inserted into the tube stock 1 and the double pipe is formed by expanding both a taper part 2 and a large diameter part 4. At this time, the double pipe is formed by integrally forming the clamp die and the punch and passing the tube stock 1 through the clearance between the taper hole and punch of the clamp die. Next, a turned-down part 26 is formed by turning down the end of the large diameter part 4 to the outside. Thence, a double-pipe part 38 is formed by expanding the large diameter part 4 and bringing the same into close contact with the inner periphery of the turned-down part 26. The taper angle of the taper part 2 is formed at an angle at which the axial load of the tube stock 1 is reduced and is formed to the taper angle of the product after the formation of the double-pipe part 38.