In an SOR exposure system for transferring patterns on masks to semiconductor wafers by using SOR light reflected by an X-ray reflecting mirror, a first shutter device for shielding at least .gamma. rays and a second shutter device for shielding X-rays are provided between the SOR ring and the mirror inside a beam port, and an exposure adjustment device for adjusting the amount of exposure when a circuit pattern on a mask is transferred to a wafer is provided between the mirror and the wafer. As a result, the human body can be protected against radiation rays, such as gamma rays, generated from the SOR ring when electrons are implanted thereto or when the SOR ring is stopped. Damage to the X-ray reflecting mirror caused by radiation rays is reduced, and stable reflectance of the mirror can be obtained. Maintenance of the SOR exposure system is also made easier.