Welding device and welding method

A welding device for welding stacked materials to each other that contain a thermoplastic resin, the welding device comprising:

• a first unit;
• a second unit, the materials being interposed between the first unit and the second unit;
• wherein the first unit includes a first heating unit configured to come into contact with one of the materials, and a first mold arranged with the first heating unit,
• wherein the second unit includes a second heating unit configured to come into contact with another of the materials, and a second mold arranged with the second heating unit,
• wherein the first heating unit and the second heating unit each have a sheet-like heat generating body configured to generate heat by electric power, insulating layers interposing the heat generating body therebetween, and a contact layer on which the insulating layers interposing the heat generating body therebetween are laminated, and
• wherein the contact layers are provided in the first heating unit and the second heating unit, each having thermal conductivity of 10 W/m×K or greater at normal temperature and Young's modulus of 30 GPa or greater at normal temperature.