PURPOSE: To provide the sterilizing device capable of smoothly sterilizing the inside of a safety cabinet outside a working space after working.

CONSTITUTION: Air is forcibly fed by a fan 11 to a high-performance filter 9 for an air feeding on one side of the working space 6. The other side of the working space 6 is provided with discharge holes 12, 13 through which the air in the working space 6 passes. A communicating path 7 for passing the air flowing out of the working space 6 through these discharge holes 12, 13 is disposed. The leeward side of the fan 11 is provided with a discharge path 14 for discharging the air outside of the body 5 via the high-performance filter 9 for discharge. This communicating path 7 is provided with an ozone generator 22. The discharge path 14 is provided with catalysts 17. An ozone generator 22 is operated in the state of closing an opening/closing door 8 and the fan 11 is run at a low speed below the rated rotating speed. The fan 11 is run at the rated rotating speed in the state of stopping the ozone generator 22.