The utility model discloses an automatic drainage device, comprising a water inlet pipe, a water outlet pipe, a water receiver and a storage tank. The water inlet pipe is accessed to the water receiver. The water receiver is provided with a drainage pump. The drainage pump and the storage tank are communicated through the water outlet pipe. The operation of the drainage pump is controlled by a water level inductor. The drainage pump is provided with an independent power supply, and the water level inductor is a float. The automatic drainage device is suitable for matching with the products such as refrigerator, display cabinet and the like, which needs to drain water. Because the discharge pump is provided with the independent power supply, as long as the water in the water receiver reaches to a certain height, the float can start the operation of the drainage pump and drains the water to the storage tank. The installation of the machine is not longer limited to the sewage, and the drained water is stored in the storage tank and can be used for irrigating and cleaning, therefore the secondary use of the water can be realized.