PURPOSE: To successively, rapidly and sharply stamp the same mark on the individual surfaces of a plurality of strip like piece groups by moving one marker left and right with respect to the individual strip like pieces of the strip like piece groups to set a stamping position and subsequently moving the same up and down to perform stamping.

CONSTITUTION: An unvulcanized rubber compd. is formed into a wide and long rubber compd. sheet by a sheet molding roll 2. A plurality of slits 20 are provided to the rubber compd. sheet in the longitudinal direction thereof while the sheet is sent out continuously to constitute a group of a plurality of strip like pieces 1 arranged side by side. One marker 5 is moved left and right with respect to the individual strip like peaces 1 of the strip like piece group to set a stamping position and subsequently moved up and down to perform stamping. By this constitution, the same mark can be stamped on the individual surfaces of a plurality of the strip like pieces successively, rapidly and sharply.