The protective cover puts on the outside of the camera, making the inside of the protective cover form an inclosed space so as to prevent the damage of the monitor parts caused by the sanility and moisture infiltrated from the outside. Moreover, the gas is filled the inside of the protective cover, and the gas pressure inside the cover is larger than the air pressure outside the cover in order to stop the entering of the combustible gases. Thus, it avoids the firing caused by the spark generated by the electric components inside so as to raise the security and prolong the service life. |