A washing machine includes: a tub and a detergent supply device which supplies a liquid additive to the tub, wherein the detergent supply device includes: a cartridge containing the additive; a check valve assembly including a check valve for controlling extracting of the additive, and a check valve housing forming a space in which the extracted additive is temporarily stored; a pump for extracting the additive by changing a pressure in the space; and an outlet passage through which the temporarily stored additive is discharged, wherein the check valve assembly comprises a first outlet opening communicating with the cartridge, a second outlet opening communicating with the outlet passage, a first check valve for opening and closing the first outlet opening, and a second check valve for opening and closing the second outlet opening, wherein the first and second check valves are opened in the same direction.