The electromotive force is caused if the point of the thermocouple is heated with the burner, and the current flows to the coil of the magnet unit. Under such a condition, the contact pole piece of the magnet unit is pressed against the magnet by the push rod and it absorbs the magnet by magnetism. Even if release the push rod the gas passage will keep opening. Under such a condition, the thermocouple point gets cold when the flame disappears, and the electromotive force is not caused. The valve doesn't adsorb contact pole piece by magnet, and the gas passage is intercepted by valve returned with the elasticity of spring.