Method of manufacturing variable wall thickness steel pipe and variable wall thickness steel pipe

A method of manufacturing a variable wall thickness steel pipe with a hollow tubular raw pipe, the method comprising:

• locking the raw pipe in a die by thrusting a plug into the raw pipe from an one end side, so as to expand an outer shape on the one end side, in a state where the raw pipe is disposed inside the die and movement of the raw pipe in a longitudinal direction is restricted;
• and
• performing ironing in which an inner shape of the raw pipe is expanded while the outer shape is maintained so that a thin portion is formed by further thrusting the plug toward the other end side of the raw pipe while the locked state of the raw pipe is maintained, whereas the movement of a portion of the other end side of the raw pipe is unrestricted so that the portion of the other end side of the raw pipe is elongated in the longitudinal direction,
• thereby obtaining the variable wall thickness steel pipe.