A fuel cell system includes a fuel cell stack generating electric power using an electrochemical reaction between hydrogen and oxygen, a fuel process unit supplying reformed gas to the fuel cell stack by reforming an electricity generation material into the reformed gas that is rich in hydrogen, and an air supply unit supplying air containing oxygen to the fuel cell stack. The air supply unit includes an intake passage that extends from an outside space to the fuel cell stack, a first air pump that is installed on the intake passage to allow the air to be introduced into the fuel cell stack, and a first pressure buffer container that is disposed between the first air pump and the fuel cell stack to reduce pressure of the air flowing along the intake passage to a level less than a predetermined pressure.