A method of controlling an air conditioner includes a step of sensing the capacitance of condensed water through a plurality of electrode pads to sense the level of condensed water stored in a condensed water storage part during cooling, a step of comparing the sensed level of the condensed water with a drainage level stored in a memory, and a step of, upon determining that the sensed level of the condensed water is within an error range of the drainage level, operating a drainage pump. A water level detecting device of the air conditioner more accurately senses the level of condensed water based on the capacitance of the condensed water, thereby effectively controlling the drainage pump.