An apparatus, for use in vehicles, for detecting a harmful gas material surrounding the apparatus to then adequately ventilate a surrounding air comprises a case which is equipped with a sensor utilizing an electric measuring device. The sensor, in contact with a surrounding air through an air passage, is mounted on a connection portion of an electric circuit board and is protruded from the case to a chamber. The chamber has a set of holes and is formed on a case cover, the set of holes of the chamber being provided with a set of corresponding filters. The air passage is formed between an inner and an outer walls of a case cap covering the chamber.
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