A fuel cell system comprising: a reformer that reforms raw fuel to generate fuel gas; and a plurality of fuel cells of solid oxide that generates electric power by using said fuel gas and oxidant gas, wherein said plurality of fuel cells is arranged in an up-down direction and a right-left direction, and said reformer has a cell facing face that faces any of said plurality of fuel cells in a back-and-forth direction, characterized in that a fuel cell assembly is supported by an assembly supporter, and said fuel cell assembly includes: two or more fuel cells that are arranged adjacent to one another among said plurality of fuel cells; a fuel gas common supply pipe that is connected to each of said two or more fuel cells and through which said fuel gas that is supplied from said reformer to said two or more fuel cells flows; a negative electrode exhaust gas common exhaust pipe that is connected to each of said two or more fuel cells and in which negative electrode exhaust gas exhausted from said two or more fuel cells is collected; an oxidant gas common supply pipe that is connected to each of said two or more fuel cells and through which said oxidant gas that is supplied to said two or more fuel cells flows; and a positive electrode exhaust gas common exhaust pipe that is connected to each of said two or more fuel cells and in which positive electrode exhaust gas exhausted from said two or more fuel cells is collected. a reformer that reforms raw fuel to generate fuel gas; and a plurality of fuel cells of solid oxide that generates electric power by using said fuel gas and oxidant gas, wherein said plurality of fuel cells is arranged in an up-down direction and a right-left direction, and said reformer has a cell facing face that faces any of said plurality of fuel cells in a back-and-forth direction, characterized in that a fuel cell assembly is supported by an assembly supporter, and said fuel cell assembly includes: two or more fuel cells that are arranged adjacent to one another among said plurality of fuel cells; a fuel gas common supply pipe that is connected to each of said two or more fuel cells and through which said fuel gas that is supplied from said reformer to said two or more fuel cells flows; a negative electrode exhaust gas common exhaust pipe that is connected to each of said two or more fuel cells and in which negative electrode exhaust gas exhausted from said two or more fuel cells is collected; an oxidant gas common supply pipe that is connected to each of said two or more fuel cells and through which said oxidant gas that is supplied to said two or more fuel cells flows; and a positive electrode exhaust gas common exhaust pipe that is connected to each of said two or more fuel cells and in which positive electrode exhaust gas exhausted from said two or more fuel cells is collected. two or more fuel cells that are arranged adjacent to one another among said plurality of fuel cells; a fuel gas common supply pipe that is connected to each of said two or more fuel cells and through which said fuel gas that is supplied from said reformer to said two or more fuel cells flows; a negative electrode exhaust gas common exhaust pipe that is connected to each of said two or more fuel cells and in which negative electrode exhaust gas exhausted from said two or more fuel cells is collected; an oxidant gas common supply pipe that is connected to each of said two or more fuel cells and through which said oxidant gas that is supplied to said two or more fuel cells flows; and a positive electrode exhaust gas common exhaust pipe that is connected to each of said two or more fuel cells and in which positive electrode exhaust gas exhausted from said two or more fuel cells is collected.