PURPOSE: To ensure the detection of ozone with a simple constitution and to enhance reliability by providing the constitution wherein cracks are formed in a base member when corrosion progresses due to the reaction with the ozone, and a conducting film is broken.

CONSTITUTION: A thin base member 6 comprises a material with less ozone- proof property wherein cracks are formed by the reaction with ozone. A conducting film 7 which is broken by the occurrence of the cracks in the member 6 is laminated on the base member 6. An electric circuit 8 whose conduction is cut off by the breakdown of the conducting film 7 due to the occurrence of the cracks in the member 6 is provided on both sides of the direction of the length of the conducting film 7. The circuit 7 detects the ozone through lead wires 71 which are connected to both end parts of the conducting film 7. Then, the thin base member 6 is corroded by the reaction of the ozone. The conducting film 7 is broken by the occurrence of the cracks. Thus, the ozone can be detected with the simple constitution, and the reliability can be enhanced.