A safety cabinet is capable of preventing ozone gas from leaking out of a working chamber during decontamination and circulating the ozone gas in the working chamber to decontaminate the working chamber. The safety cabinet includes a cabinet main body； a shutter that allows opening/closing of an opening part communicatively connecting to a working chamber； an exhaust path through which gas is exhausted from the working chamber； an exhaust valve that is provided in the exhaust path； an air supply and circulating fan that is provided in the working chamber； an ozone generator that introduces ozone gas into the working chamber； a control part that controls the exhaust valve； an air supply and circulating fan； and airtightly closing device that allows the shutter to airtightly close the opening part are included. The gas in the working chamber is made internally circulatable, so that the ozone gas can be prevented from leaking out, and the ozone gas can be internally circulated in the working chamber to decontaminate the working chamber with the ozone gas at a set CT value.
