Reflection surfaces and a diaphragm for limiting light fluxes disposed between an object and the reflection surface that is located closest to the object are provided. The deaerator 2 further includes gas partial pressure variation suppression means 23A, 23B, 23C, 25Ab, 25Bb, 25Cb, 29A, 29B, and 29C for suppressing variations in partial pressures of a specific gas in the reduced-pressure spaces 25A, 25B, and 25C. If the destination server has provided no synchronization point, the starting synchronization point is generated by a source server indicating its desired type identifier, target state, and current key.