There is provided a heartbeat detection device. The heartbeat detection device includes a time difference value calculation unit (3) configured to calculate a time difference value from a sampling data string of an electrocardiographic waveform of a living body, an index value calculation unit (4) configured to calculate an index value for heartbeat detection based on the time difference value, a threshold setting unit (5) configured to determine whether a peak of the index value exceeding a threshold can be detected, to calculate, when not less than a predetermined number of peaks is consecutively detected, a threshold candidate based on an average value of the predetermined number of the most recent peaks among these peaks, not to update the threshold when the threshold candidate exceeds a threshold limit value based on a difference limit value that is likely be a time difference value of the electrocardiographic waveform of the living body, and to set the threshold candidate as a new threshold when the threshold candidate has a value equal to or less than the threshold limit value, and a heartbeat time determination unit (6) configured to set the sampling time of the peak as the heartbeat time when the peak of the index value exceeding the threshold is detected.