Injection device (2, 3), in particular for injecting a fluid into an exhaust tract of an internal combustion engine, having a flexible diaphragm which is mechanically connected to an armature which is movable between at least one first position and at least one second position, an elastic element which is designed and arranged to push the armature in the direction of a second position; and an actuator which is designed and arranged such that the armature can, by activation of the actuator, be moved from a second position in the direction of a first position counter to the force of the elastic element, wherein the diaphragm delimits a pressure chamber which can be filled with fluid via a fluid line and a one-way valve which prevents a backflow of fluid from the pressure chamber into the fluid line, the volume of which pressure chamber is variable by movement of the diaphragm; characterized - in that the injection device has an injection unit with a nozzle body, wherein - an injection chamber connected to the pressure chamber is formed in the nozzle body; wherein - on an end face of the nozzle body, there is formed an injection opening through which, during an injection process, the fluid can escape from the injection chamber, wherein - a nozzle needle is arranged in the injection chamber, which nozzle needle is movable between a closure position, in which one end of the nozzle needle closes the injection opening, and an opened position, in which the nozzle needle opens up the injection opening, wherein - at an end face, averted from the injection opening, of the nozzle needle, there is formed a control chamber connected to the fluid line, the volume of which control chamber is variable by movement of the nozzle needle between the closure position and the opened position; wherein - the nozzle needle is movable between the closure position and the opened position by means of a pressure difference between the control chamber and the injection chamber; and wherein - the one-way valve, the pressure unit with the pressure chamber and the injection unit with the injection chamber and the movable nozzle needle are integrated in a common injection device. - in that the injection device has an injection unit with a nozzle body, wherein - an injection chamber connected to the pressure chamber is formed in the nozzle body; wherein - on an end face of the nozzle body, there is formed an injection opening through which, during an injection process, the fluid can escape from the injection chamber, wherein - a nozzle needle is arranged in the injection chamber, which nozzle needle is movable between a closure position, in which one end of the nozzle needle closes the injection opening, and an opened position, in which the nozzle needle opens up the injection opening, wherein - at an end face, averted from the injection opening, of the nozzle needle, there is formed a control chamber connected to the fluid line, the volume of which control chamber is variable by movement of the nozzle needle between the closure position and the opened position; wherein - the nozzle needle is movable between the closure position and the opened position by means of a pressure difference between the control chamber and the injection chamber; and wherein - the one-way valve, the pressure unit with the pressure chamber and the injection unit with the injection chamber and the movable nozzle needle are integrated in a common injection device.