To provide a charged particle beam exposure system which immediately detects the attachment of foreign substances onto a reticle.

The charged particle beam exposure system has an arrangement wherein a light beam 15 passes through a space above the reticle 4 in parallel with the reticle 4. Accordingly, the foreign substance 17 unavoidably passes through the light beam 15 before attaching to the reticle 4, diffusing light. Thus, by detecting the diffused light 18 with a detector 19, it is turned out that the foreign substance 17 has attached to the reticle 4. Once the attachment of the foreign substance 17 onto the reticle 4 is confirmed through a signal from the detector 19, exposure is interrupted to convey the reticle 4 to a cleaning device for cleaning.