PURPOSE: To lengthen the length of a tube stock possible to be formed by mounting one of outside and inside tube bodies on a moving frame body and the other on a fixed frame and constituting a bellows forming pressure means and a tube stock sending means of a moving hydraulic cylinder possible to move the moving frame body in the lengthwise direction.

CONSTITUTION: Fixed side split dies 10, 10' with on-off hydraulic cylinders 8, 8' are mounted on the fixed frame 31. Moving side split dies 11, 11' are mounted on the moving frame body 28. A forming pressure hydraulic means 6 and an annular seal hydraulic means 15, 16 are composed of the outside tube body 19, the inside tube body 20 and a central tube body 22. One of the outside and inside tube bodies 19, 20 is mounted on the moving frame body 28 and the other is on the fixed frame 31. The bellows forming pressure means and the tube stock sending means are made of the moving hydraulic cylinder 26 possible to move in the lengthwise direction. In this way, the moving hydraulic cylinder can play two parts of pressing the side of the bulging part of the tube stock and sending out the tube stock.