A gas supply system appropriate for an abdominal cavity and a luminal cavity is provided. The gas supply system reduces a pressure of gas, supplied from a source of gas for supplying gas of a predetermined kind, to a predetermined pressure value upon which gas, whose pressure is reduced, is controllably lowered to a first pressure value appropriate for a body cavity of a first kind of a specimen to allow gas to be supplied to the body cavity of the first kind. In the meantime, gas, supplied from the source of gas, is lowered to a second pressure value appropriate for a body cavity of a second kind of the specimen to allow gas to be supplied to the body cavity of the second kind.
