PURPOSE: To automatically stop a flow of gas by melting plastic fluidized to move to a porous unit side, charging the inside of a porous unit with the plastic, and generating plugging in this porous unit, in the case that a temperature of gas piping rises to a melting temperature or more of the molten plastic.

CONSTITUTION: A substrate 1, deformed to soften or changed into a viscous fluid a temperature rise, is set up in a gas flow path in a condition that the flow path of gas is ensured, and also a heat resistant porous material 2, formed into a knitting ball shape, is arranged in the vicinity of a part of arranging the substance deformed to soften in the gas flow path. In the case of generating a hazardous condition by a temperature rise in the gas flow path, the substance 1, deformed to soften or fluidized viscous by the temperature rise, is moved by a pressure of gas to a side of the porous material 2, and by plugging it, the gas flow path is closed. Thus when a gas transport path is placed in a hazardous condition by the temperature rise due to breaking-out of fire, etc., the gas transport path is automatically closed to prevent the breaking out of the fire and its spread before occurrence.