Abstract: A respiratory function measuring device comprises: a three-dimensional measuring unit that measures a chest movement and an abdomen movement of a breathing animal; a first measuring unit that measures a time T1 where a rate of volume decrease of the abdomen is maximized in an expiration; a second measuring unit that measures a time T2 where a rate of volume decrease of the chest is maximized in the expiration; and a respiratory time difference outputting unit that computes and outputs a value Tde corresponding to T2-T1. This allows measuring respiratory function to diagnose an obstructive pulmonary disease, a restrictive pulmonary disease, and the like in a natural state, for a subject of a breathing animal, even if the subject does not have a sense of self-awareness.