PURPOSE: To simply and inexpensively provide an explosion-proof band of sturdy construction by caulking and jointing both ends of a trip metal sheet with a caulking tool having a cylindrical punch section and a die section having a ring groove at the inner bottom thereof for coupling the punch section.

CONSTITUTION: Both ends 2 and 3 of a metal sheet 1 are superposed on top of each other and, then, placed on the die section 11 of a caulking tool 7. Thereafter, a punch 9 is pressed and fitted thereto. As a result, a punch section 8 pushes both ends 2 and 3 into a die section 10, and a part of the end 3 is also pushed into a ring groove 12, thereby performing a deep drawing process. In addition, when the punch 9 is further pressed, the end 2 expands externally within the die section 10, thereby performing a caulking process. A structure so formed has sufficient shear strength and peel strength, and the joint strength thereof is extremely high. According to this construction, the number of caulking sections can be reduced, compared with the case of spot welding. Also, a joint section is free from deterioration and rust. At the same time, a work becomes easy and a welding facility is not needed, thereby ensuring low construction cost.