This invention relates to a ventilation system which assures a superior safety by suppressing a localized stagnation of a flammable gas and a concentration increase thereof in case a leakage of a flammable gas or refrigerant is detected. The ventilation system is comprised of a detector which detects a flammable gas or refrigerant, a ventilating fan which ventilates a room, a ceiling fan and an air conditioner indoor unit which stir the air of the room, en electric power supply switch which turns off a power supply to a fan heater or an electric stove. With this configuration, in the room, a localized stagnation of the gas can be avoided and a source of fire can be eliminated; thereby, a superior safety can be realized.