A device for monitoring the blood pressure of a living subject, including a pulse-wave-propagation-velocity-relating information obtaining device for successively obtaining pulse-wave-propagation-velocity-relating information which relates to a pulse-wave propagation velocity at which a pulse wave propagates in an artery of the subject, a pulse-period-relating information obtaining device for successively obtaining pulse-period-relating information which relates to a pulse period of the subject, a peripheral-blood-volume-relating information obtaining device for successively obtaining peripheral-blood-volume-relating information which relates to a volume of blood which flows in a peripheral body portion of the subject, and an abnormality judging device for judging that the blood pressure of the subject is abnormal when at least one of the pulse-wave-propagation-velocity-relating information, pulse-period-relating information, and peripheral-blood-volume-relating information does not fall within a corresponding one of a first, a second and a third reference range.