A washing machine comprising: a main body in which an inlet is formed in a front portion thereof; a tub provided inside the main body, wherein a main water supply port configured to receive water from an external water source, a main drain port configured to discharge water, and an inlet port through which water is received from a sink are formed in the tub; a washing tub rotatably provided inside the tub; a sink (60, 560) provided on the main body and having a water tank formed to be recessed to store water, wherein the water tank includes a soaking part in which laundry is soaked and a scrubbing part adapted for scrubbing and hand-washing of laundry, and wherein an auxiliary drain port through which water in the sink is discharged is formed in the soaking part; and a drain device configured to control a discharge of the water stored in the sink (60, 560) to the inlet port of the tub, wherein the drain device comprises: a main drain pipe configured to discharge water in the tub, a drain pump provided in the main drain pipe to pump water, an auxiliary drain pipe to fluidly connect the sink and the tub, wherein one end of the auxiliary drain pipe is connected to the auxiliary drain port of the sink and other end of the auxiliary drain pipe is connected to the inlet port of the tub; and a drain valve configured to open or close the auxiliary drain port and the auxiliary drain pipe. a main body in which an inlet is formed in a front portion thereof; a tub provided inside the main body, wherein a main water supply port configured to receive water from an external water source, a main drain port configured to discharge water, and an inlet port through which water is received from a sink are formed in the tub; a washing tub rotatably provided inside the tub; a sink (60, 560) provided on the main body and having a water tank formed to be recessed to store water, wherein the water tank includes a soaking part in which laundry is soaked and a scrubbing part adapted for scrubbing and hand-washing of laundry, and wherein an auxiliary drain port through which water in the sink is discharged is formed in the soaking part; and a drain device configured to control a discharge of the water stored in the sink (60, 560) to the inlet port of the tub, wherein the drain device comprises: a main drain pipe configured to discharge water in the tub, a drain pump provided in the main drain pipe to pump water, an auxiliary drain pipe to fluidly connect the sink and the tub, wherein one end of the auxiliary drain pipe is connected to the auxiliary drain port of the sink and other end of the auxiliary drain pipe is connected to the inlet port of the tub; and a drain valve configured to open or close the auxiliary drain port and the auxiliary drain pipe. a main drain pipe configured to discharge water in the tub, a drain pump provided in the main drain pipe to pump water, an auxiliary drain pipe to fluidly connect the sink and the tub, wherein one end of the auxiliary drain pipe is connected to the auxiliary drain port of the sink and other end of the auxiliary drain pipe is connected to the inlet port of the tub; and a drain valve configured to open or close the auxiliary drain port and the auxiliary drain pipe.