PURPOSE: To provide the method and device for measuring heartbeat rate so as to measure the heartbeat of a reagent under exercise from measured pulses while fitting a photointerrupter to the forehead of the reagent especially concerning the device and method for measuring heartbeat for measuring heartbeat under exercise.

CONSTITUTION: A sensor part equipped with a light emitting element 21 and a light receiving element 22 is mounted to the forehead of the reagent, and a pulse frequency detecting means 2 measures the pulse frequency of the reagent. Further, a vibration detecting means 3 measures the vibrations of the vertical action of the reagent, and an operation processing means 5 calculates an average pulse frequency from the measured pulse frequency and calculates the heartbeat of the reagent from these values by using a prescribed calculating formula.