Provided is a respiratory state estimating device including a pulse wave signal acquiring unit that acquires a pulse wave signal from a portion of a living subject, a pulse rate calculating unit that calculates a pulse rate of the living subject based on the pulse wave signal, and a respiratory state estimating unit that estimates a respiratory state of the living subject based on the pulse rate. Also, provided is a respiratory state estimating method including optically acquiring a pulse wave signal from a portion of a living subject, calculating a pulse rate of the living subject based on the pulse wave signal, estimating a respiratory state of the living subject from the pulse rate.