To reduce the replacement frequency of a prefilter and to reduce the possibility of contamination caused by replacement in a safety cabinet equipped with the prefilter and an HEPA filter.

A working space 3 is formed in a body case 1a of the safety cabinet 1, and a front shutter 4 is arranged in an openable/closable manner on the front side. The HEPA filter 12 and a blower 12 are arranged in an HEPA filter suction side space 12a, and the prefilter 18 is arranged upstream of the HEPA filter. The prefilter is a sheet-like filter wound in roll shape, and one end is wound around a delivery part, while the other end is wound around a winding part. A planar filter medium surface is formed in the middle of the delivery part and winding part. Either the delivery part or the winding part is provided with a handle 17 for turning the prefilter from the outside of the working space to renew the filter medium surface.