A washing machine has a structure to facilitate the supply of a liquid detergent. A detergent supply device of the washing machine includes a valve housing in communication with a detergent container, a valve housing cap coupled to the valve housing and provided with an opening, a plunger configured to pass through the opening and disposed inside the valve housing to be guided by the valve housing cap, and a sealing configured to surround a circumference of the plunger to selectively open and close the opening according to the movement of the plunger.