In a heartbeat measurement device of the related art, in the case where the level of a heartbeat waveform signal of a living body obtained from a sensor is low, a peak cannot be determined or the arithmetical processing employed is complex and the device is lacking in convenience. With the present invention, the maximum value M of a heartbeat signal obtained at a predetermined time interval is detected by maximum value detecting means, and in the case where, in the processing of S11 and S14, a maximum value M that is larger than the detected maximum value M is not detected within a fixed time period T1, in the processing of S15, the maximum value M detected by the maximum value detecting means is determined to be a peak value P. Then, the heart rate is calculated by calculating means on the basis of a time interval T2 between successive peak values P determined by the peak value determining means. In addition, in accordance with the time interval T2 between successive peak values P determined by the peak value determining means, the fixed time period T1 is successively changed in the processing of S3 to S10 to a corresponding one of a plurality of time periods predetermined in accordance with the time interval T2 between the peak values P.
