To provide an developing device with which developing is executable under the structure for mass production.

By providing a base stock setting table 5 on which a material W to be developed is set and a rotatable roller 22 for imparting clamping force by bringing into tight contact with the material W to be developed and making the base stock setting table 5 and roller 22 relatively movable in the length direction of the material W to be developed, the bended part (a) or the curved part (b) of the material W to be developed is continuously clamped in the length direction. Supporting parts 12, 13 whose ascending and descending action is controllable and with which both sides for clamping the bended part (a) of the base stock W are supported from the lower part are provided, by controlling the ascending and descending action of the supporting parts 12, 13, the height position of the bended part (a) of the base stock W is composed so as to be adjusted in the position of a prescribed clamping height with upper and lower dies 7, 9.