The wearable measurement device includes a mounting part for mounting the device to a human body, a variation detection part detecting a variation in distance from a predetermined portion of the human body, a posture detection part detecting a posture of the variation detection part in the case where the device is mounted to the human body through the mounting part, and a measurement part measuring the number of predetermined motions based on the variation detected by the variation detection part and the posture detected by the posture detection part. The variation detection part includes a light emitting unit and a light receiving unit, makes the light emitting unit emit light and the light receiving unit detect reflection light reflected at a predetermined portion, detects a distance from the predetermined portion and outputs an electric signal (voltage or current) in accordance with the detected distance at a predetermined sampling cycle.
