PROBLEM TO BE SOLVED: To provide a drain plug capable of simplifying installation work and adjustment work of a detected water level and inexpensively detecting the water level. SOLUTION: A drainage water level adjusting section capable of adjusting a vertical height from a rice field, a water level controlling section for automatically adjusting a vertical height of the drainage water level adjusting section via an actuator, the water level controlling section and an external device. Is a drain plug that adjusts the stored water level in the field, and moves up and down in conjunction with the drain water level adjusting unit, and the relative field relative to the drain water level adjusting unit. A first water level sensor for measuring the water level is provided. [Selection diagram] Fig. 3【課題】設置作業や検出水位の調整作業が簡素化され、しかも安価に水位を検出可能な排水栓を提供する。【解決手段】田面からの上下高さを調節可能な排水水位調節部と、アクチュエータを介して前記排水水位調節部の上下高さを自動調整する水位制御部と、前記水位制御部と外部装置とを接続する無線通信部とを備えて構成され、圃場の貯水水位を調節する排水栓であって、前記排水水位調節部と連動して上下し、前記排水水位調節部を基準とする圃場の相対水位を測定する第１の水位センサを備えている。【選択図】図３
