PURPOSE: To measure a reflection attenuation quantity in a short time by utilizing a speaker as a driving source for expanding or contracting a fiber.

CONSTITUTION: An optical fiber 11 to be expanded or contracted is fixed to an optical fiber fixing section 13 at two positions by means of a bonding agent 14 by leaving a part in the specific length, e.g. about 70cm. The part of specific length of the optical fiber 11 is strained in parallel by means of a circular optical fiber support member 12. A vibration section of a speaker 15 is fixed to the optical fiber fixing section 13. The speaker 15 is driven by an oscillator 16 with a voltage having a saw-tooth-wave or a triangle wave. Therefore, the optical fiber 11 is expanded or contracted by means of the speaker 15 and the length of the optical fiber which is expanded or contracted is twice the amplitude of the speaker 15. The speaker 15 may have a rated input of about 10 W and the oscillator 16 may have a maximum output of about 10 V×1 A so that it is possible to generate well enough a strain force of 1 N. Thus, it is possible to measure a reflection attenuation quantity in a short time.