Simple and small-sized equipment which continuously afford alternate twists to an optical fiber and a method using the apparatus are provided. The equipment includes: a guide roller for causing the fiber to roll; a roller supporting member for holding the roller in a manner allowing the roller to freely turn about an axial center X; and a driving unit to cause the roller to oscillate by making the supporting member to turn about an axial center Y that is inclined relative to the axial center X. The method includes: arranging a guide roller to intersect the fiber, the roller being held by a roller supporting member to freely turn about an axial center X; oscillating the roller by driving the supporting member to revolve about the axial center Y which is inclined relative to the axis center X; and causing the fiber to roll to afford alternate twists to the fiber.