To offer a respiration detector in which dust enters between a mobile electrode and a non-movable electrode with external air circulating through an external respiration detector to cause neither a glitch nor poor measuring, its measurement precision is sustained even if it is employed over a long time, and moreover, failure cannot easily happen.

The respiration detector (9) is equipped with a mobile electrode (9c) moving with working with displacement of a diaphragm separating gas for respiration and the external air, which spread pressure fluctuation generated when a person breathes, by a pressure difference between the gas for respiration and the external air, a non-movable electrode (9d) arranged in an opposing relation to the mobile electrode (9c), an open air through hole (H) bored in the non-movable electrode in order to freely circulate in relation to the diaphragm the external air through the non-movable electrode (9d), and a filter (9e) mounted on the prestage side of the open air through hole (H) on a pathway, through which the external air circulates, to eliminate dust contained in the external air.