A fuel cell module comprising: a fuel cell stack having a stack body in which a plurality of flat plate-shaped fuel cells adapted to generate electrical power by an electrochemical reaction between a fuel gas and an oxygen-containing gas are stacked; and a start-up combustor adapted to generate a combustion gas for raising a temperature of the fuel cells; wherein the fuel cell stack includes: end plates (50, 52) that are disposed on an upper end side and a lower end side of the fuel cells, apply a clamping load to the fuel cells in a stacking direction of the fuel cells, and are larger in size in a planar direction than the fuel cells; a side wall that is formed between an outer peripheral portion of the upper-end-side end plate and an outer peripheral portion of the lower-end-side end plate over an entire perimeter of the outer peripheral portions and seals the fuel cells; an oxygen-containing gas introduction passage through which the oxygen-containing gas flows, the oxygen-containing gas introduction passage being formed in a space between the fuel cells and the side wall; and an oxygen-containing gas introduction port formed on a side portion of the fuel cells, and through which the oxygen-containing gas introduction passage and an oxygen-containing gas flow field for supplying the oxygen-containing gas to a cathode are in communication with each other, whereby the oxygen-containing gas introduction port introduces into the oxygen-containing gas flow field of the fuel cells the oxygen-containing gas of the oxygen-containing gas introduction passage; and the start-up combustor is arranged in an interior of the fuel cell stack, in a manner so as to face toward a side portion of the fuel cells where the oxygen-containing gas introduction port is formed, on an oxygen-containing gas pathway between the oxygen-containing gas introduction passage and the oxygen-containing gas introduction port. a fuel cell stack having a stack body in which a plurality of flat plate-shaped fuel cells adapted to generate electrical power by an electrochemical reaction between a fuel gas and an oxygen-containing gas are stacked; and a start-up combustor adapted to generate a combustion gas for raising a temperature of the fuel cells; wherein the fuel cell stack includes: end plates (50, 52) that are disposed on an upper end side and a lower end side of the fuel cells, apply a clamping load to the fuel cells in a stacking direction of the fuel cells, and are larger in size in a planar direction than the fuel cells; a side wall that is formed between an outer peripheral portion of the upper-end-side end plate and an outer peripheral portion of the lower-end-side end plate over an entire perimeter of the outer peripheral portions and seals the fuel cells; an oxygen-containing gas introduction passage through which the oxygen-containing gas flows, the oxygen-containing gas introduction passage being formed in a space between the fuel cells and the side wall; and an oxygen-containing gas introduction port formed on a side portion of the fuel cells, and through which the oxygen-containing gas introduction passage and an oxygen-containing gas flow field for supplying the oxygen-containing gas to a cathode are in communication with each other, whereby the oxygen-containing gas introduction port introduces into the oxygen-containing gas flow field of the fuel cells the oxygen-containing gas of the oxygen-containing gas introduction passage; and end plates (50, 52) that are disposed on an upper end side and a lower end side of the fuel cells, apply a clamping load to the fuel cells in a stacking direction of the fuel cells, and are larger in size in a planar direction than the fuel cells; a side wall that is formed between an outer peripheral portion of the upper-end-side end plate and an outer peripheral portion of the lower-end-side end plate over an entire perimeter of the outer peripheral portions and seals the fuel cells; an oxygen-containing gas introduction passage through which the oxygen-containing gas flows, the oxygen-containing gas introduction passage being formed in a space between the fuel cells and the side wall; and an oxygen-containing gas introduction port formed on a side portion of the fuel cells, and through which the oxygen-containing gas introduction passage and an oxygen-containing gas flow field for supplying the oxygen-containing gas to a cathode are in communication with each other, whereby the oxygen-containing gas introduction port introduces into the oxygen-containing gas flow field of the fuel cells the oxygen-containing gas of the oxygen-containing gas introduction passage; and the start-up combustor is arranged in an interior of the fuel cell stack, in a manner so as to face toward a side portion of the fuel cells where the oxygen-containing gas introduction port is formed, on an oxygen-containing gas pathway between the oxygen-containing gas introduction passage and the oxygen-containing gas introduction port.