Abstract: A monitoring device includes a receiving unit, a processing unit, and an information providing unit. The receiving unit is configured to receive a first photoplethysmogram signal acquired by irradiating a body of a subject with a first light having a first wavelength, and a heartbeat signal corresponding to a heartbeat of the subject. The processing unit is configured to calculate a fundamental frequency of heart rate corresponding to a heart rate of the subject based on the heartbeat signal, and estimate a fundamental frequency of pulse rate of the subject by comparing the fundamental frequency of heart rate with a frequency component of the first photoplethysmogram signal. The information providing unit is configured to provide information acquired based on the fundamental frequency of pulse rate.