A device for metering anesthetic is provided such that a new anesthetic is immediately available for the metering when the anesthetic is changed. The metering device has an assembly unit that can be removed from the medical apparatus as a module with a reservoir (4) for a liquid anesthetic, an intermediate container (9) arranged downstream of the reservoir (4), a metering gas source (11) connected to the intermediate container (9) and a metering element (14) for anesthetic on the discharge side of the intermediate container (9). An evaporator chamber (15) may be provided for evaporating the metered anesthetic. A connecting device lets through at least anesthetic vapor as an interface between the assembly unit (1) and the medical apparatus (2).