PROBLEM TO BE SOLVED: To provide a novel heartbeat measurement method and heartbeat measurement device, capable of measuring heartbeat of a sleeper with an excellent detection accuracy without attaching a special device to a body or exerting binding force to the body.SOLUTION: The heartbeat measurement method measuring heartbeat of a sleeper using a pressure detection element group arranged on a pressure acting surface of the sleeper includes: a body pressure information acquisition step detecting body pressure distribution information of the sleeper from the pressure detection element group; a respiratory pressure information acquisition step detecting pressure fluctuation distribution information corresponding to a respiratory cycle of the sleeper by the pressure detection element group; an element selection step selecting a heartbeat measurement element in the pressure detection element group using at least one of the body pressure distribution information acquired in the body pressure information acquisition step and the pressure fluctuation distribution information acquired in the respiratory pressure information acquisition step; and a heartbeat detection step detecting a pressure fluctuation corresponding to the cardiac cycle of the sleeper by the heartbeat measurement element selected in the element selection step.