A washing machine comprising: a tub storing water; a drum rotatably provided in the tub and accommodating laundry; and a detergent supply device supplying a liquid additive to the tub, wherein the detergent supply device comprises: a plurality of cartridges containing the additive respectively; a plurality of check valve assemblies which are connected to the plurality of cartridges respectively to control extracting of the additive, wherein the check valve assemblies have a check valve housing (410, 460) forming a space in which the extracted additive is temporarily stored; a pump extracting the additive from the plurality of cartridges by changing a pressure of the space of the check valve housing (410, 460) of the plurality of check valve assemblies; a water supply valve receiving water from an external water source; and an outlet pipe having a plurality of check valve connection pipes respectively connected to the plurality of check valve assemblies, and through which the water supplied from the water supply valve and the additive extracted from the cartridge flow, wherein the plurality of check valve assemblies comprise: a first discharge hole communicating with the cartridge and formed in the check valve housing (410, 460); a second discharge hole communicating with the outlet pipe and formed in the check valve housing (410, 460); a first check valve for opening and closing the first discharge hole; and a second check valve for opening and closing the second discharge hole, wherein the first and second check valves (420, 470) are opened in the same direction. a tub storing water; a drum rotatably provided in the tub and accommodating laundry; and a detergent supply device supplying a liquid additive to the tub, wherein the detergent supply device comprises: a plurality of cartridges containing the additive respectively; a plurality of check valve assemblies which are connected to the plurality of cartridges respectively to control extracting of the additive, wherein the check valve assemblies have a check valve housing (410, 460) forming a space in which the extracted additive is temporarily stored; a pump extracting the additive from the plurality of cartridges by changing a pressure of the space of the check valve housing (410, 460) of the plurality of check valve assemblies; a water supply valve receiving water from an external water source; and an outlet pipe having a plurality of check valve connection pipes respectively connected to the plurality of check valve assemblies, and through which the water supplied from the water supply valve and the additive extracted from the cartridge flow, wherein the plurality of check valve assemblies comprise: a first discharge hole communicating with the cartridge and formed in the check valve housing (410, 460); a second discharge hole communicating with the outlet pipe and formed in the check valve housing (410, 460); a first check valve for opening and closing the first discharge hole; and a second check valve for opening and closing the second discharge hole, wherein the first and second check valves (420, 470) are opened in the same direction. a plurality of cartridges containing the additive respectively; a plurality of check valve assemblies which are connected to the plurality of cartridges respectively to control extracting of the additive, wherein the check valve assemblies have a check valve housing (410, 460) forming a space in which the extracted additive is temporarily stored; a pump extracting the additive from the plurality of cartridges by changing a pressure of the space of the check valve housing (410, 460) of the plurality of check valve assemblies; a water supply valve receiving water from an external water source; and an outlet pipe having a plurality of check valve connection pipes respectively connected to the plurality of check valve assemblies, and through which the water supplied from the water supply valve and the additive extracted from the cartridge flow, wherein the plurality of check valve assemblies comprise: a first discharge hole communicating with the cartridge and formed in the check valve housing (410, 460); a second discharge hole communicating with the outlet pipe and formed in the check valve housing (410, 460); a first check valve for opening and closing the first discharge hole; and a second check valve for opening and closing the second discharge hole, wherein the first and second check valves (420, 470) are opened in the same direction. a first discharge hole communicating with the cartridge and formed in the check valve housing (410, 460); a second discharge hole communicating with the outlet pipe and formed in the check valve housing (410, 460); a first check valve for opening and closing the first discharge hole; and a second check valve for opening and closing the second discharge hole, wherein the first and second check valves (420, 470) are opened in the same direction.