A washing machine includes a main body; a washing tub, and a detergent supply device configured to supply detergent to the washing tub. The detergent supply device includes a detergent housing disposed in the main body and formed with a flow path through which the detergent is suppliable to the washing tub; a detergent case to be disposed inside the detergent housing, to store the detergent inside therein, and formed with a detergent outlet through which the detergent stored inside the detergent case is discharged; and a detergent pump to be connected to the detergent outlet to supply the detergent stored in the detergent case to the flow path, and the detergent case includes a guide member and the detergent outlet of the detergent case is coupleable to the guide member which covers a part of an upper portion of the detergent outlet while coupled to the detergent outlet.