To provide a technique capable of bonding housing members constructing a housing body with high bonding strength.

An air injection hole-forming part 510 forms an air injection hole 228 in the first sheet 220 by a boring punch 240. The first sealing part 550 bonds the first sheet 220 and the second sheet 230 such that a housing space 10a is formed by a lower housing surface 223 of the first sheet 220 and an upper housing surface 233 of the second sheet 230, and that an air passage 213 is formed between the air injection hole 228 and the housing space 10a. The air injection part 560 injects the air from the air injection hole 228 to make the pressure of the inside of the housing space 10a not less than the atmospheric pressure. The air passage shielding part 570 temporarily shields the air passage 213 on the housing space 10a side by a press member 270. The second sealing part 580 bonds a position from the shielding position to the air injection hole 228 side.