A device for calculating a pulse period of a living body. The device includes a maximum value detecting unit that detects a maximum value of a biological signal received at a predetermined time interval, a peak value determining unit that determines whether the maximum value is a peak value of the biological signal detected by the maximum value detecting unit during a fixed time period, a calculating unit that calculates a rhythmic pulse period of a living body generating the biological signal based on a time interval between successive peak values of the biological signal and a fixed time period changing unit that changes the fixed time period to a predetermined time period that corresponds to the time interval between the successive peak values of the biological signal.
