To effectively restrain hunting of chamber pressure control means.

This chamber pressure control system has the chamber pressure control means 6B, 9A and 9B for adjusting chamber pressure (p) of an object chamber 1 to target chamber pressure ps by adjusting a balance between an air supply quantity and an air exhaust quantity to the object chamber 1, and is provided with a system preserving means 11 for changing an operation characteristic of the chamber pressure control means 6B, 9A and 9B to another characteristic from a present characteristic when the hunting is caused by detecting generation of the hunting H in the chamber pressure control means 6B, 9A and 9B.