To provide a washing machine which can reuse a substituted gas.

A washing system 1 of the first embodiment comprises a washing tank 310, a supply means, a discharge means and a nitrogen separator 420 in a washing system 1 which washes washed objects 600 with carbon dioxide of supercritical or liquid state. The washing tank 310 contains the washed objects 600. The supply means feeds nitrogen for substituting for the gas in the washing tank 310 to the washing tank 310. The discharge means discharges a mixed gas containing nitrogen and the gas in the washing tank 310 out of the washing tank 310. The nitrogen separator 420 is arranged in the discharge means and separates nitrogen from the mixed gas.