To provide an etching method which can perform etching of an optical fiber while controlling the diameter dimension of the optical fiber.

The etching method comprises the following: an optical fiber is immersed in an etching solution, and signal light is caused to be incident from a light source upon one end of the optical fiber, propagated through the core inside of the optical fiber, and caused to go out of the other end; the decay of power of the signal light at the time of its going out is measured in comparison with the power of the signal light at the time of its being incident; and when the variation of the decay reaches a predetermined value while being measured, the immersed optical fiber is pulled up from the etching solution to end the etching.