A fuel cell system comprising: a fuel cell that generates electrical power with oxidant and fuel; and a burner in which anode off-gas discharged from an anode of the fuel cell and cathode off-gas discharged from a cathode of the fuel cell burn, wherein: the burner includes anode off-gas apertures from which the anode off-gas is ejected, and first cathode off-gas apertures and second cathode off-gas apertures from which the cathode off-gas is ejected, and in a cross section of the burner at a cutting plane that passes one of the first cathode off-gas apertures, one of the anode off-gas apertures, and one of the second cathode off-gas apertures that are aligned on a straight line when the burner is seen in plan view, the one of the first cathode off-gas apertures is provided on one of opposite sides of the one of the anode off-gas apertures such that a vector of an ejecting direction of the cathode off-gas from the one of the first cathode off-gas apertures forms a first acute angle (θ1) with a vector of an ejecting direction of the anode off-gas from the one of the anode off-gas apertures, and the one of the second cathode off-gas apertures is provided on another of the opposite sides of the one of the anode off-gas apertures such that a vector of the ejecting direction of the cathode off-gas from the one of the second cathode off-gas apertures forms a second acute angle (θ2) with the vector of the ejecting direction of the anode off-gas, wherein the burner includes: an annular anode off-gas wall surface having the anode off-gas apertures, the anode off-gas apertures being formed at a predetermined interval in a circumferential direction of the annular anode off-gas wall surface; an annular first cathode off-gas wall surface having the first cathode off-gas apertures, the first cathode off-gas apertures being formed at a predetermined interval in a circumferential direction; and an annular second cathode off-gas wall surface having the second cathode off-gas apertures, the second cathode off-gas apertures being formed at a predetermined interval in a circumferential direction. a fuel cell that generates electrical power with oxidant and fuel; and a burner in which anode off-gas discharged from an anode of the fuel cell and cathode off-gas discharged from a cathode of the fuel cell burn, wherein: the burner includes anode off-gas apertures from which the anode off-gas is ejected, and first cathode off-gas apertures and second cathode off-gas apertures from which the cathode off-gas is ejected, and in a cross section of the burner at a cutting plane that passes one of the first cathode off-gas apertures, one of the anode off-gas apertures, and one of the second cathode off-gas apertures that are aligned on a straight line when the burner is seen in plan view, the burner includes anode off-gas apertures from which the anode off-gas is ejected, and first cathode off-gas apertures and second cathode off-gas apertures from which the cathode off-gas is ejected, and in a cross section of the burner at a cutting plane that passes one of the first cathode off-gas apertures, one of the anode off-gas apertures, and one of the second cathode off-gas apertures that are aligned on a straight line when the burner is seen in plan view, the one of the first cathode off-gas apertures is provided on one of opposite sides of the one of the anode off-gas apertures such that a vector of an ejecting direction of the cathode off-gas from the one of the first cathode off-gas apertures forms a first acute angle (θ1) with a vector of an ejecting direction of the anode off-gas from the one of the anode off-gas apertures, and the one of the second cathode off-gas apertures is provided on another of the opposite sides of the one of the anode off-gas apertures such that a vector of the ejecting direction of the cathode off-gas from the one of the second cathode off-gas apertures forms a second acute angle (θ2) with the vector of the ejecting direction of the anode off-gas, wherein the burner includes: an annular anode off-gas wall surface having the anode off-gas apertures, the anode off-gas apertures being formed at a predetermined interval in a circumferential direction of the annular anode off-gas wall surface; an annular first cathode off-gas wall surface having the first cathode off-gas apertures, the first cathode off-gas apertures being formed at a predetermined interval in a circumferential direction; and an annular second cathode off-gas wall surface having the second cathode off-gas apertures, the second cathode off-gas apertures being formed at a predetermined interval in a circumferential direction. an annular anode off-gas wall surface having the anode off-gas apertures, the anode off-gas apertures being formed at a predetermined interval in a circumferential direction of the annular anode off-gas wall surface; an annular first cathode off-gas wall surface having the first cathode off-gas apertures, the first cathode off-gas apertures being formed at a predetermined interval in a circumferential direction; and an annular second cathode off-gas wall surface having the second cathode off-gas apertures, the second cathode off-gas apertures being formed at a predetermined interval in a circumferential direction.