An exhaust gas processing device for a fuel cell is disclosed. In the exhaust gas processing device, hydrogen gas purged from the fuel cell is mixed with cathode exhaust gas from the fuel cell and diluted prior to being discharged to an atmosphere. The exhaust gas processing device includes a reservoir in which purged hydrogen gas from the fuel cell is retained and mixed with cathode exhaust gas from the fuel cell, and an agitating gas introduction inlet provided at an upper part of the reservoir. The purged hydrogen gas is mixed with and diluted by agitating gas introduced from the agitating gas introduction inlet.