This paper proposes an unconstrained measurement system of person’s heartbeat under walking. This system uses a cloth like a vest which has a built-in phonocardiographic (PCG) sensor. With the system, the PCG sensor extracts the person’s heartbeat signal through a vibration of the sensitive element of the sensor and then the periods of heartbeat and walking are simultaneously measured by a pattern matching between the filtered output of the sensor and a linear combination of the sinusoidal functions reflecting the two periods of the heartbeat and walking.