A fuel cell system includes a fuel cell, a fuel gas supply line, an oxidizing agent gas supply line, a fuel gas discharge line, and a reformer provided in the fuel gas supply line. A first circulating line circulates the fuel gas from the fuel gas discharge line to an upstream side of the reformer in the fuel gas supply line as a first circulating gas. The circulation device is provided in the fuel gas supply line, and suctions the first circulating gas by using the flow of the fuel gas flowing through the fuel gas supply line as a driving flow. A second circulating line circulates the fuel gas from a downstream side of the circulation device in the fuel gas supply line or the fuel gas discharge line to the upstream side of the circulation device in the fuel gas supply line as a second circulating gas.