The inkjet printer for labelling goods has a writing head (20) which has a at least one outlet opening (26) for ink droplets, b a printing unit (78) which is connected to said outlet opening, c a compressed air pump (70) and d an electric controller (32). It has at least one storage vessel (40) for liquid which flows through the outlet opening. The storage vessel is connected releasably to the writing head in a coupling region. A first pressure sensor (80) is arranged on the compressed air line (76) in the writing head, which first pressure sensor (80) detects the air pressure in the compressed air line and outputs an air pressure signal to the controller (32). A second pressure sensor is arranged on the ink line, which second pressure sensor detects the pressure in the ink line and outputs an ink pressure signal to the controller. The latter outputs an "Ink empty" signal if the ink pressure signal drops by more than 10% with respect to the air pressure signal.