A cutting tool includes a steel gear-shaped cutter which has cutting edges for die-cutting a fiber mat into a predetermined gear shape. The cutting edges include tooth-top, tooth-bottom and tooth-surface cutting edges, and. The cutter has an inclined cylindrical exterior shape so that its thickness gradually increases from the cutting edges toward the base end. V-shaped grooves are formed on the exterior surface and become shallower from the cutting edge toward the base end. The wedge angle (α1) of the tooth-bottom line from the tooth-bottom cutting edge to the base end is greater than the wedge angle (α2) of the tooth-top cutting edge surface from the tooth-top cutting edges to the base end. The thickness (W1) of the tooth-bottom cutting edge is greater than the thickness (W2) of the tooth-top cutting edge on the base-side end.