PURPOSE: To manufacture cores which are excellent in the flexibility and bend formability, by connecting numerous core pieces formed by making slits in a beltlike metallic plate to a wire having slacked sections and by stretching the slacked sections, when cores for welt are manufactured.

CONSTITUTION: Slits 7 which intermittently extend in the width direction of a beltlike metallic plate 2 through a connecting section 6, are formed at constant intervals in the lengthwise direction of the metallic plate 2, and thus numerous core pieces 8 are formed. A wire 9 having slacked sections 9a is put on the upper or the lower surface of the core pieces 8 and the core pieces 8 are welded to the wire 9 by spot welding. After the core pieces 8 are fixed to the wire 9, the connecting section 6 is cut and the core pieces 8 are separated from each other. By stretching the slacked sections 9a of the wire 9, spaces 10 are formed between cores 8, and thus cores 11 for welt which are excellent in the flexibility and bend formability are inexpensively manufactured with an excellent material yield.