[Problem] To provide a method for measuring biological activity caused by respiration for which the conditions for measuring biological activity are not easily influenced by the surrounding environment. [Solution] Provided is a method for measuring biological activity caused by subject respiration. The biological activity measurement method includes (a) a step of disposing at least one absorbing element having an absorption rate no less than a prescribed value in a position where body movement occurs that accompanies subject respiration, (b) a step of an imaging device generating a video comprising a plurality of frame images by way of receiving light, a portion of which is absorbed by the at least one absorbing element and the remaining portion of which is reflected by the subject or the at least one absorbing element, (c) and a step of an image processing circuit measuring biological activity caused by respiration of the subject on the basis of the luminance information of the plurality of frame images.
