To provide a welded zone shaping method, a shaping tool and a shaping apparatus, capable of shaping a welded zone with a small shaping load, without causing complication in process and in apparatus configuration.

A welding device 10 includes: the shaping tools 12, 13 equipped with a thin plate 45, a distortion gauge 47 for detecting the distortion of the thin plate 45, a thermocouple 48 for detecting the temperature of the thin plate 45, and a cavity 46 with the distortion gauge 47 and the thermocouple 48 disposed thereon; a driving mechanism 18 for moving the respective parts 40 to 42 of the shaping tools 12, 13 forward and backward relative to the welded zone 60 in the direction orthogonal to a butting direction; a butt adjusting mechanism 19 for adjusting the butting load of welding members 30a, 30b; and a control unit 50 for obtaining the respective detection results from the distortion gauge 47 and the thermocouple 48, and upon deciding that the welded zone 60 is half-solidified higher than an A3 transformation point based on the detection results, controlling the driving mechanism 18 and the but adjusting mechanism 19 to shape the welded zone 60.