A washing machine and a method of controlling the washing machine are provided. In the washing machine and the method of controlling the washing machine, a liquid detergent is automatically supplied into a washing tub, thereby improving user convenience. In addition, in the washing machine and the method of controlling the washing machine, a liquid detergent is supplied into the washing tub by water circulated by a circulation unit. Thus, no liquid detergent remains in a liquid detergent supply path, and the liquid detergent supply path can be prevented from being blocked due to the solidification of a liquid detergent.