Abstract: The invention provides a measuring apparatus for measuring small liquid flows, particularly in the medical sector. The measuring apparatus comprises a siphon unit as a liquid flow sensor, a measuring chamber being located in its retention area. As soon as the liquid supplied to the measuring chamber reaches a given liquid level, the measuring chamber is automatically emptied by the siphon effect. The emptied liquid volume is fixed and constant. The emptying is determined by an optical detector means in the vicinity of the measuring chamber and/or upstream of the outflow area of the siphon unit.