To inhibit a small animal, such as a mouse, from intruding a casing of an electric equipment enclosure, without using a specialized electric wire.

An ozone generator for the electric equipment enclosure has an ozonizer 3 positioned in the electric equipment enclosure, wherein the ozonizer 3 continuously or intermittently emits ozone so that a concentration of the emitted ozone is not lower than a concentration at which the small animal is repelled but lower than another concentration which is harmful to the human body and equipment installed in the enclosure. The ozone is continuously emitted so that its concentration is higher than the concentration at which the mouse is repelled, and is harmless to the the human body or lower than the concentration at which the equipment and wires inside the electric equipment enclosure are corroded. Because the ozone spontaneously disappears, the concentration is not raised after elapsing of a certain time, so that the equipment is not damaged. The concentration of the emitted ozone is set according to a size of the casing of the electric equipment enclosure.