A fuel cell stack includes a plurality of fuel cells stacked via separators, each one of which cells has a solid electrolyte plate interposed between an anode electrode and a cathode electrode. The separator is constituted of an uneven member that includes a first abutting portion, a second abutting portion, and a connecting portion, the first abutting portion abuts on one fuel cell of the two adjacent fuel cells, the second abutting portion abuts on the other fuel cell, and the connecting portion connects the first abutting portion to the second abutting portion. At least one abutting portion of the first abutting portion or the second abutting portion has a section modulus greater than a section modulus of the connecting portion.