PURPOSE: To make it possible to operate the system in a natural circulation manner by providing a hot air supply path for supplying heated air from a heating part into the room and opening the lower end of the rise-up part of the leading end thereof to the heating part side.

CONSTITUTION: A heat exchange part 4 and an exhaust part 3 are provided at the intermediate of a suction path 2, and a hot air supply path 6 for supplying heated air from a heating part 1 to respective rooms 5. The flow of air heats air at the heating part 1 and when air is supplied through the hot air supply path 6 into each room 5, since the leading end of the hot air supply path 6 forms a rise-up part 14, air warmed at the heating part 1 advances through a heated air inlet port 20 at the lower end of the rise-up part 14 and rises up due to the difference in specific gravity. By the flow of air produced upon this occasion, hot air can be supplied into respective rooms 5 by natural circulation. By the difference in the specific gravity of air produced upon this time, and the entire system of central heating or ventilation can be conducted in a natural circulation system.