Disclosed is a single facer for producing a plurality of types of single-faced corrugated paperboard sheets having different flute configurations. The single facer of the present invention comprises: a plurality of corrugating roll pairs; a plurality of cartridges each pivotally supporting a pair of corrugating rolls arranged in an up-down direction in a respective one of the corrugating roll pairs, each of the cartridges being selectively serving as an operational cartridge supporting one of the corrugating roll pairs located in an operational position, and a rest cartridge supporting one of the corrugating roll pairs located in a rest position; and a single facer body having a frame structure internally formed with a transfer space for the cartridges, wherein the operational cartridge is disposed above the rest cartridge in such a manner that the operational cartridge is supported from therebelow by the rest cartridge.