A washing machine comprising: a tub configured to accommodate washing water therein; and a drain pump (100, 100a, 100b) configured to pump the washing water in the tub, wherein the drain pump comprises: a washing water inlet compartment; a drain pump compartment configured to pump washing water contained in the washing water inlet compartment to an outside; a pumping motor coupled to the drain pump compartment; a suction port provided between the washing water inlet compartment and the drain pump compartment to move the washing water from the washing water inlet compartment to the drain pump compartment; and a drain line (60, 60a, 60b) connecting from the drain pump compartment to an outside to discharge the washing water; and an air outlet port provided on an upper portion of the drain pump compartment to discharge air contained in the drain pump compartment to an outside; characterized by an air inlet port (61 a) provided on the drain line, and an air passage (170a,b) connecting the air outlet port to the air inlet port (61 a) such that air flows from the air outlet port to the air inlet port due to the difference in pressure between the air outlet port and the air inlet port caused by a velocity of the washing water at the drain hose being higher than he velocity of the washing water in the drain pump compartment and thus the pressure in the pump case being higher than the pressure in the drain hose. a tub configured to accommodate washing water therein; and a drain pump (100, 100a, 100b) configured to pump the washing water in the tub, wherein the drain pump comprises: a washing water inlet compartment; a drain pump compartment configured to pump washing water contained in the washing water inlet compartment to an outside; a pumping motor coupled to the drain pump compartment; a suction port provided between the washing water inlet compartment and the drain pump compartment to move the washing water from the washing water inlet compartment to the drain pump compartment; and a drain line (60, 60a, 60b) connecting from the drain pump compartment to an outside to discharge the washing water; and a washing water inlet compartment; a drain pump compartment configured to pump washing water contained in the washing water inlet compartment to an outside; a pumping motor coupled to the drain pump compartment; a suction port provided between the washing water inlet compartment and the drain pump compartment to move the washing water from the washing water inlet compartment to the drain pump compartment; and a drain line (60, 60a, 60b) connecting from the drain pump compartment to an outside to discharge the washing water; and an air outlet port provided on an upper portion of the drain pump compartment to discharge air contained in the drain pump compartment to an outside; characterized by an air inlet port (61 a) provided on the drain line, and an air passage (170a,b) connecting the air outlet port to the air inlet port (61 a) such that air flows from the air outlet port to the air inlet port due to the difference in pressure between the air outlet port and the air inlet port caused by a velocity of the washing water at the drain hose being higher than he velocity of the washing water in the drain pump compartment and thus the pressure in the pump case being higher than the pressure in the drain hose.