Separator unit and fuel cell stack

A separator unit is inserted between adjacent stacked fuel cells, in each of which an electrolyte layer is sandwiched between a fuel electrode and an oxygen electrode. The separator unit includes a sheet-shaped gas barrier member, which blocks a gas, and a collector, which is inserted between the gas barrier member and the fuel electrode or the oxygen electrode and which is provided with a plurality of openings that diffuse the gas. The collector is provided with an electrode contact portion, which is made up of a flat, porous panel that is in contact with the fuel electrode or the oxygen electrode and collects power, and a gas barrier member contact portion, which is made up of a linear piece that forms a gas flow route by being in contact with the gas barrier member and supports the electrode contact portion. A height dimension of the gas barrier member contact portion is smaller than an equivalent diameter of an opening in the electrode contact portion.