To eliminate the requirement for a positioning pin to protrude/retract, to inexpensively construct a forming device in a simple manner, and to restrict any positional deviation of the plate-shaped workpiece for achieving the high forming accuracy.

A plate-shaped workpiece 16 is highly accurately positioned by a pilot opening 20b formed in a center part in the longitudinal direction, and since the hot pressing is performed while pilot openings 20a-20c including the pilot opening 20b are engaged with positioning pins 22a-22c, the forming accuracy is enhanced. Since the hot pressing is performed while pilot openings 20a-20c are engaged with positioning pins 22a-22c, the cycle time is shortened and forming efficiency is improved, and the maintenance burden is reduced according to the reduction of the number of movable parts, and the forming cost is also reduced. Meanwhile, since the positioning pins 22a-22c can be integrally fixed to a lower press die 12, the forming device can be inexpensively constructed in a simple manner.