FUEL CELL STACK

A fuel cell stack includes stacked cells, each including a sheet-shaped power generation portion, two separators, a gas passage defining plate that includes a gas passage portion through which reactant gas flows, and a frame member that includes a supply port and a discharge port. The gas passage portion includes opposing portions extended in a flow direction of the reactant gas and arranged in parallel in an orthogonal direction. A main passage is defined between each opposing portion and the power generation portion. The gas passage portion includes a first passage portion adjacent to the supply port in the flow direction and a second passage portion adjacent to the first passage portion in the orthogonal direction. The main passages of the second passage portion each have a larger cross-sectional flow area than the main passages of the first passage portion.