PURPOSE: To obtain the precent device, hygienically formable a wrapping bag for a triangular rice-ball, by laying an inner bag and sheetlike food on an intermittently moving triangular base board, wrapping an outer bag, and welding the open edges of the inner and outer bag.

CONSTITUTION: Inner bags 101 are laid one by one on a base board 82 by an inner bag supplying device 5 during cessation of the triangular base board 82 at the inner bag supplying station S1. At a sheetlike food supplying station S2, the inner bag 101 is covered with a triangularly folded sheetlike food 106 by a sheetlike food supplying device 2 and at an outer bag supplying station S3, an outer bag 102 is laid on the sheetlike food, then at a bag welding station S4, the inside surface of an open edge of the outer bag 102 and the outer surface of an open edge of the inner bag 101 are welded by a welding device 9.