Abstract: An apparatus is proposed for the dosed dispensing of a fluid, especially an infusion fluid, comprising a housing (1) with a fluid chamber and a pressure medium chamber (3) by which a flexible wall (4) of the fluid chamber can be pressurized from the outside with a pressure medium. In order to provide a re-useable infusion pump with especially simple means it is proposed that the housing (1) consists of two mutually detachably joined housing parts (6, 7), of which the one comprises the pressure medium chamber (3) and the other receives in an exchangeable manner the fluid chamber configured as a leak-proof infusion bag (2), and that the housing part (6) with the pressure medium chamber (3) is sealed by a membrane (5) against the housing part (7) receiving the infusion bag (2) and is connected to a gas pressure source (11).