An exhaust system capable of diluting a hydrogen gas to a concentration below the lower explosive limit without requiring a large amount of dilution gas while preventing an increase in a pressure of an exhaust gas in a buffer tank is disclosed. The exhaust system performs, when a main valve disposed in an exhaust line is closed, an initial exhaust operation in which a gas heavier than the hydrogen gas is discharged from a lower part of a buffer tank while an inlet valve disposed in an inlet line and a first outlet valve disposed in an outlet line are opened to introduce the exhaust gas from an equipment in a tangential direction of a buffer tank. Next, the exhaust system performs a hydrogen-gas discharge operation in which the inlet valve and the first outlet valve are closed, and the a bypass valve disposed in a bypass line and the second outlet valve disposed in a hydrogen-gas discharge line are opened to discharge the hydrogen gas stayed in an upper part of the buffer tank while flowing the exhaust gas into a bypass line.