A slider (12) is mounted to a cutter body (2) of an optical fiber cutter (1) in a forward/backward movable state. A round blade member (19) for forming shear marks on an optical fiber is rotatably mounted onto the slider (12). An operation lever pin (29) for changing over rotation operation modes from one to another is mounted onto one end side of a pin member penetrating through a wall part (26) of the cutter body (2). The rotating actions modes relates to a non-rotation mode, a constant rotation mode and a single-turn rotation mode, wherein the non-rotation mode is used for preventing the round blade member (19) from being rotated; the constant rotation mode is used for causing the round blade member (19) to be rotated a predetermined angle every time the slider (12) moves backward; and the single-turn rotation mode is used for causing automatically switching to the non-rotation mode after the round blade member (19) is rotated only a single turn at the predetermined angle when the slider (12) moves backward.