To provide a siphon groundwater level control system which can efficiently control the groundwater level of the whole field by enhancing drainability when the water level is high as in the case of heavy rain.

In this siphon groundwater level control system, a siphon pipe for discharging service water from a culvert pipe to a drain pipe is installed between the culvert pipe buried in the field and the drain pipe communicating with a drainage canal. The siphon pipe portion includes: a first cornice pipe which is vertically provided on the side of the culvert pipe; a second cornice pipe which is vertically provided on the side of the drain pipe; an upper connecting pipe for connecting the upper end of the first cornice pipe and that of the second cornice pipe together; and a water level regulating means for regulating the vertical position of the upper connecting pipe.