The apparatus for generating a mixture of reducing agent and air has a pumping agent feed pump having a pump housing and a mixing chamber into which reducing agent and air pumped by the feed pump can be introduced; the mixing chamber is embodied in a mixing chamber body which communicates directly with the pump housing of the feed pump and forms a cap of the pump housing. The feed pump has a drive shaft which protrudes into the pump housing, and the mixing chamber body is disposed at least approximately radially to the drive shaft The apparatus has a compact structural size and only a slight reducing agent-filled idle volume.