PURPOSE: To manufacture reinforcing bars which provides reinforcing ribs to a steel plate without troublesome operations of welding, or eliminates the troublesome operations of joining by wires or welding.

CONSTITUTION: A plurality of groove parts 15-17 whose sectional shape is approximate to that of the products stepwise along the feeding direction of a slab 8 are provided at least to either of both dies 6, 7. Thus, by approximately setting the shapes of the dies 6, 7, ribs are formed by putting the excessive thickness during the press operation of the slab 8 into the groove part stepwise, or by forming the hole to the stab 8 at the part other than the groove part and stepwise enlarging this hole, the slab 8 is formed in a net-shaped manner at the groove part.