The present invention provides an automatic fire extinguishing device that can detect a fire at the temperature lower than 120 degrees Celsius and that can be installed for a long term in a state of maintenance-free. The fire extinguishing device consists of a pressure resistant container (10) filled with an extinguishant and a pressurization agent, an container valve (12) attached to the opening of the pressure resistant container (10), and an fire detection tube (14) connected to the container valve (12). The fire detection tube (14) is formed with the lamination of a tubular base resin layer and an gas barrier layer, the base resin layer is made of a thermoplastic resin and the gas barrier layer is made of ethylene vinyl alcohol copolymer resin (EVOH resin).