PURPOSE: To improve the dispersing property and bonding property to concrete of a product by providing an inclined part having a proper condition on either cutting edge face of a fixed cutting edge and a movable cutting edge of a cutter in a manufacturing device of metal staples used for fiber reinforced concrete.

CONSTITUTION: A thin steel plate 3 is cut into a determined width by a slitter roller 1 and sent to a cutter 7. The cutter 7 has a vertically moving upper cutting edge 8 and a fixed lower cutting edge 9, with the lower cutting edge 9 having a plane edge face 9a. The edge face 8a of the upper cutting edge 8 has a ridgeline form having recessed parts composed of a first inclined part 11 and a second inclined part 10 bisymmetrically with the central plane part 12 as the boundary. Each dimension of the upper cutting edge 8 is determined under the conditions of 2°≤θ1≤30°, 45°≤θ2≤80°, L0≥W, W-10≤L1≤W-2mm (W is the width of the thin steel plate). The metal staple cut by lowering the upper cutting edge 8 has a form in which the both ends are looped and the center part is recessed, and this form provides excellent dispersing property and bonding property to concrete.