PURPOSE: To continuously cut a traveling optical fiber into uniform lengths by moving the edge of a rotary knife in a circular arc at the same speed as the traveling optical fiber to scratch the optical fiber and bending the optical fiber to open the scratch.

CONSTITUTION: An optical fiber 1 is traveled by a driving roller 6, and the fiber 1 is traveled while slightly deflecting the fiber 1 by rollers 7a, 7b, 7c and 7d. Supporting arms 2a and 2b furnished with a circular rotary knife 5 is rotated, the edge of the knife 5 is moved in a circular arc at the same speed as the traveling fiber 1, the fiber 1 is traveled on the tangent to the circular arc, and the fiber 1 is scratched. The fiber is then bent to open the scratch, and the fiber 1 is cut.