PURPOSE: To permit cutting or trimming along a camber by distributing cutting margin correctly and uniformly at right and left along the camber of a strip, thus executing oscillation independently on each milling machine, in trimming or finishing at the both edge parts in the direction of width of the strip.

CONSTITUTION: A side guide 17 for positioning is arranged on the input side with respect to the direction of flow of a strip 15 which is drawn-out by a pinch roll 16, and a single pair or plural pairs of milling machines 19 are arranged on the output side. A detection head 28 is arranged on the input side and an auxiliary roller 30 is arranged on the output side, each integrally with the cutting head 22 of a working machine 19. The position of the strip is detected by the head 28 and the roller 30 independently, and oscillation is executed independently on each working machine 19, and the strip is guided, following a camber.