To facilitate exchange of an exposed part and an unexposed part by forming side edges of a clamping plate to clamp the plate edge from the back side to cover the blade tip of the plate edge so that the exposed part and the unexposed part of the blade tip are mutually repeated and equipping pressing parts protruded from the sides of the clamping plate on the plate edge.

A spare edge 10 comprises a long plate blade 1 and a clamping plate 2 which is formed so as to be possible to clamp the plate edge from the back side X. The clamping plate 2 is formed rather short so that one end side does not reach the blade tip 3 and the other end side 4 is formed in a wave shape and the edge tip 3 covered by the wave shape end side 4 is made so that the exposed part and the unexposed part are mutually repeated at equal pitches L. On the side end part 1' of the plate edge 1 is cut in a corner shape at the corner of the edge tip 3 so that only the side end part in the back side is remained to be formed as a pressing part 5 in a protruding shape. The pressing part 5 is pressed to exchange the exposed part A and the unexposed part B.