A fuel cell system includes a fuel cell stack formed by stacking a plurality of power generation cells, and an ejector for supplying a fuel gas to the fuel cell stack. A flow rectifier for rectifying the flow of the fuel gas is provided at a portion of an insulating plate of the fuel cell stack connecting the ejector and the fuel gas supply passage. The flow rectifier includes an opening having a laterally elongated shape in correspondence with the bottom of the fuel gas supply passage having a laterally elongated shape, and a plurality of holes provided above the opening.