A continuous measurement in a house employs demand controlled ventilation system, whose terminal devises change its opening area by sensing relative humidity of internal area, was executed in an inhabited condition. Temperature, relative humidity, carbon dioxide concentration, air flow rate & power input of ventilation system and so on were obtained. Measured results show air flow rate of ventilation system is changed by relative humidity proportionally, operating specific fan power is smaller than reference value of Energy Saving Code of Japan, and formaldehyde concentration is low enough even when air flow rate was lessened in winter.