To provide a method of forming a zone to be laser-welded of a plated steel plate and its device that a cost for forming a projecting part constituting a zone to be laser-welded is decreased.

The forming device 30 is provided with a press 50 fixed to the tip of a robot arm composed of a first to a fourth arms 42, 44, 46 and 48 in shaping robots 32a and 32b. The press 50 is provided with a punch and a die, and a projecting and a recessing mold parts are formed on the punch and the die, respectively. A pressure is applied on the punch and the die by a cylinder, and a projecting part is formed on a work clamped between the punch and the die by the projecting and the recessing mold parts.