PURPOSE: To reduce operating time without requiring a measurement of a depth of groove, by coining a mark simultaneously, in coining a groove for bending in a metallic sheet by means of a coining tool.

CONSTITUTION: A projecting part 6 for coining a groove and a projecting part 7 for coining a mark are respectively formed in one side face of a coining tool 5. In a case of coining a groove 9 for bending in a thin metallic sheet 8 by the coining tool 5, the groove 9 having a prescribed depth is automatically obtained when a mark 10 is coined in the metallic sheet 8. Thus the need for a measurement depending on such as conventional projector a measuring instrument equipped with a dial gauge etc. is eliminated, and the operating time is reduced.