Fuel cell system and exhaust gas treatment device

An exhaust gas treatment device comprising:

• an outer housing including a first inflow part into which first exhaust gas is introduced, and a second inflow part into which second exhaust gas is introduced;
• an inner housing provided in the outer housing and having a gas inflow part into which the first exhaust gas and the second exhaust gas are introduced;
• a guide channel defined between the outer housing and the inner housing and configured to guide a part of the first exhaust gas, which is introduced into the first inflow part to the gas inflow part;
• and
• a spiral member including:
• a barrel part provided in the inner housing while communicating with the first inflow part and configured to define a passage flow path through which the first exhaust gas passes;
• a spiral protrusion provided on an outer surface of the barrel part and configured to define a spiral flow path between the barrel part and the inner housing such that the first exhaust gas and the second exhaust gas, which have passed through the gas inflow part, are mixed in the spiral flow path;
• and
• a gas discharge part provided in the barrel part and configured to discharge the first exhaust gas and the second exhaust gas, which have passed through the spiral flow path, to the passage flow path.