PURPOSE: To easily and securely finish an arm hole beautifully by providing a pressing board to be installed near the arm hole root part of a mandrel supporter, holding mechanism to displace the pressing board from an arm root adhering state to a separating state, attaching/detaching mechanism of the pressing board to the holding mechanism and iron block to press the external surface of the pressing board.

CONSTITUTION: At first, a pressing board 4 is separated from an arm root part 3 and an object 1 to be formed such as a jacket, etc., is hung over a mandrel supporter 2. Afterwards, the pressing board 4 is adhered to the arm root part 3 and between the pressing board 4 and the arm root part 3, an inner peripheral edge 40 of an arm hole A is held so as to be clipped. Then, air is sucked to the mandrel supporter 2 and the object 1 to be formed is adhered. Afterwards, the sleeve and the body of the object are pulled downward by a sleeve and body holding means and position deviation is prevented. Next, steam is jetted through an oscillating mechanism to the arm upper end part of the object 1 to be formed by the iron block and the object is pressed and formed. After forming, the iron block is separated from the object 1 to be formed and the suction of air is stopped. Then, the pressing board 4 is separated and the object 1 to be formed is detached.