A multi-unit fuel cell system that includes a common-use reforming unit configured to supply hydrogen to multiple fuel cell units that are installed in multiple units, such as apartments within an apartment building. In one example embodiment, a fuel cell system including a common-use reforming unit and multiple fuel cell units is disclosed. The common-use reforming unit is configured to supply hydrogen to the plurality of fuel cell units. Each fuel cell unit includes a stack unit, an air supplying unit, an integral heat exchange unit, a hot-water supplying unit, an auxiliary heat supplying unit, and an electric output unit.