PURPOSE: To non-intrusively measure a rhythm of a living body without giving a pain to a person to be examined, and also, without giving a hindrance to his work action in a daily work place.

CONSTITUTION: By a main sensor part 2, the heart activity potential, etc., are measured, and by a sub-sensor part 3, a disturbance element is measured. A measurement timing by each sensor 2, 3 is decided by a timer means 4, its measured data is stored time sequentially in a storage means 5, a circadian component is extracted by a circadian component extracting means 10, the influence of a disturbance is eliminated by a correcting means 6, and a rhythm carve of a living body is outputted by a rhythm curve output means 8. In such a way, a living body rhythm of a person to be examined in a daily life can be measured from the heart activity potential, etc.