A fuel cell module comprising: a fuel cell stack formed by stacking a plurality of fuel cells for generating electricity by electrochemical reactions of a fuel gas and an oxygen-containing gas; a reformer for reforming a mixed gas of water vapor and a raw fuel chiefly containing hydrocarbon to produce the fuel gas supplied to the fuel cell stack; an evaporator for evaporating water, and supplying the water vapor to the reformer; a heat exchanger for raising a temperature of the oxygen-containing gas by heat exchange with a combustion gas, and supplying the oxygen-containing gas to the fuel cell stack; an exhaust gas combustor for combusting the fuel gas discharged from the fuel cell stack as a fuel exhaust gas and the oxygen-containing gas discharged from the fuel cell stack as an oxygen-containing exhaust gas to produce the combustion gas; and a start-up combustor for combusting the raw fuel and the oxygen-containing gas to produce the combustion gas, wherein the fuel cell module includes: a first area where the exhaust gas combustor and the start-up combustor are provided; an annular second area around the first area where one of the reformer and the heat exchanger is provided; an annular third area around the second area where another of the reformer and the heat exchanger is provided; and an annular fourth area around the third area where the evaporator is provided; and wherein the heat exchanger includes an annular oxygen-containing gas supply chamber to which the oxygen-containing gas is supplied, an annular oxygen-containing gas discharge chamber to which the heated oxygen-containing gas is discharged, a plurality of heat exchange pipes connected to the oxygen-containing gas supply chamber at one end, and connected to the oxygen-containing gas discharge chamber at another end, and a combustion gas channel for supplying the combustion gas to a space between the heat exchange pipes; and at least one of the heat exchange pipes includes at least one portion where a pipe diameter is changed or a pipe cross sectional area is changed. a fuel cell stack formed by stacking a plurality of fuel cells for generating electricity by electrochemical reactions of a fuel gas and an oxygen-containing gas; a reformer for reforming a mixed gas of water vapor and a raw fuel chiefly containing hydrocarbon to produce the fuel gas supplied to the fuel cell stack; an evaporator for evaporating water, and supplying the water vapor to the reformer; a heat exchanger for raising a temperature of the oxygen-containing gas by heat exchange with a combustion gas, and supplying the oxygen-containing gas to the fuel cell stack; an exhaust gas combustor for combusting the fuel gas discharged from the fuel cell stack as a fuel exhaust gas and the oxygen-containing gas discharged from the fuel cell stack as an oxygen-containing exhaust gas to produce the combustion gas; and a start-up combustor for combusting the raw fuel and the oxygen-containing gas to produce the combustion gas, wherein the fuel cell module includes: a first area where the exhaust gas combustor and the start-up combustor are provided; an annular second area around the first area where one of the reformer and the heat exchanger is provided; an annular third area around the second area where another of the reformer and the heat exchanger is provided; and an annular fourth area around the third area where the evaporator is provided; and wherein the heat exchanger includes an annular oxygen-containing gas supply chamber to which the oxygen-containing gas is supplied, an annular oxygen-containing gas discharge chamber to which the heated oxygen-containing gas is discharged, a plurality of heat exchange pipes connected to the oxygen-containing gas supply chamber at one end, and connected to the oxygen-containing gas discharge chamber at another end, and a combustion gas channel for supplying the combustion gas to a space between the heat exchange pipes; and at least one of the heat exchange pipes includes at least one portion where a pipe diameter is changed or a pipe cross sectional area is changed. a first area where the exhaust gas combustor and the start-up combustor are provided; an annular second area around the first area where one of the reformer and the heat exchanger is provided; an annular third area around the second area where another of the reformer and the heat exchanger is provided; and an annular fourth area around the third area where the evaporator is provided; and wherein the heat exchanger includes an annular oxygen-containing gas supply chamber to which the oxygen-containing gas is supplied, an annular oxygen-containing gas discharge chamber to which the heated oxygen-containing gas is discharged, a plurality of heat exchange pipes connected to the oxygen-containing gas supply chamber at one end, and connected to the oxygen-containing gas discharge chamber at another end, and a combustion gas channel for supplying the combustion gas to a space between the heat exchange pipes; and at least one of the heat exchange pipes includes at least one portion where a pipe diameter is changed or a pipe cross sectional area is changed.