A portable breast pump has a suction unit and a collecting unit which is connected to this suction unit via a flexible suction line. The collecting unit comprises a breast shield, a milk-receiving container and a coupling element which connects the breast shield to the milk-receiving container. The suction unit has a housing with an operating means for operating the pump and a fastening means for fastening the housing on a carrying means, which can be fastened on the mother's body. This breast pump is easy to operate, allows the milk to be expressed even in confined areas with no set-down surfaces and, in addition, does not hinder the mother's mobility.