To provide a joining method of a metal sheet without generating breaking residue at joining.

This is a joining method of a metal sheet where an acute tip punch 2 is composed by forming inclining faces on a rectangular member, this punch 2 is penetrated to plural numbers of metal sheets P1, P2 lying in the laminate state, a hole (h) and a projecting piece stood with cutting on the periphery of the hole (h) are formed on respective metal sheet P1, P2, and the metal sheets P1, P2 are joined as one body by folding back the projecting pieces (s) of respective metal sheets P1, P2, so as to be lapped mutually. In this joining method, because the sheet is broken so as to be torn with cutting with the punch, the breaking residue torn off from the metal sheet is not generated, the projecting pieces are lapped surely and the metal sheets are joined surely and firmly, and the metal sheets are joined accurately without entangling the cutting scum.