PURPOSE: To improve the operation of a press forming machine by attaching both dies to the press forming machine and detaching them from it in the state that a work is between both the dies after the work is formed with an upper and lower die.

CONSTITUTION: The work W which is inserted between the upper die 12 and the lower die 11 is press formed with a pair of dies 12, 11. After that, both those dies 12, 11 are attached to the press forming machine 10 and are detached from it in the state that both the dies 12, 11 are held at the press position and that the work W is left between both the dies 12, 11 after working. Thereby, the lower die and the upper die are strongly integrated and those can be kept in the relation of the set position.