To make an assembly work easy without being required time in a frame of a device, e.g. a bag-making machine.

An end margin 4 of a second metal plate 2 is butted to one surface 3 of a first metal plate 1, and a groove 5 is made on a second metal plate 2. The groove 5 includes a wide portion 6 and a narrow portion 7. Further fastening means 11, 12 and 13 are passed through a through-hole 9 and the narrow portion 7, and engaged with the other surface 10 and the shoulder portion 8 of the first metal plate 1, and the first and second metal plates 1 and 2 are fastened and fixed by the fastening means 11, 12 and 13.