A drain pump for a laundry treating apparatus, comprising: a housing formed to have a cylindrical shape, and configured to accommodate therein washing water introduced through an inlet; a motor configured to transmit a driving force to an impeller mounted to the housing to rotate the impeller; and a circulation opening and a drain opening protruding from an outer circumferential surface of the housing in a tangential direction, forming a moving path of the washing water by being communicated with the housing, the circulation opening and the drain opening are spaced apart from each other, wherein the housing is provided with a rib protruding from one end of an inner circumferential surface of the housing towards inside of the housing, the rib is formed between the circulation opening and the drain opening, and wherein the rib is adapted to guide the washing water to the circulation opening or the drain opening, wherein a washing water flowing portion for flowing the accommodated washing water by rotation of the impeller is formed on an inner circumferential surface of the housing, characterized in that the washing water flowing portion includes: a first groove at the water flowing portion so as to be recessed towards a position communicated with the circulation opening and configured to guide a movement of liquid accommodated in the housing; and a second groove at the water flowing portion so as to be recessed towards a position communicated with the drain opening, and configured to guide a movement of liquid accommodated in the housing, wherein the first groove is formed to have a wider recessed area than the second groove to increase a washing water amount and reduce a backflow of washing water to the drain opening during a circulation process. a housing formed to have a cylindrical shape, and configured to accommodate therein washing water introduced through an inlet; a motor configured to transmit a driving force to an impeller mounted to the housing to rotate the impeller; and a circulation opening and a drain opening protruding from an outer circumferential surface of the housing in a tangential direction, forming a moving path of the washing water by being communicated with the housing, the circulation opening and the drain opening are spaced apart from each other, wherein the housing is provided with a rib protruding from one end of an inner circumferential surface of the housing towards inside of the housing, the rib is formed between the circulation opening and the drain opening, and wherein the rib is adapted to guide the washing water to the circulation opening or the drain opening, wherein a washing water flowing portion for flowing the accommodated washing water by rotation of the impeller is formed on an inner circumferential surface of the housing, characterized in that the washing water flowing portion includes: a first groove at the water flowing portion so as to be recessed towards a position communicated with the circulation opening and configured to guide a movement of liquid accommodated in the housing; and a second groove at the water flowing portion so as to be recessed towards a position communicated with the drain opening, and configured to guide a movement of liquid accommodated in the housing, wherein the first groove is formed to have a wider recessed area than the second groove to increase a washing water amount and reduce a backflow of washing water to the drain opening during a circulation process. a first groove at the water flowing portion so as to be recessed towards a position communicated with the circulation opening and configured to guide a movement of liquid accommodated in the housing; and a second groove at the water flowing portion so as to be recessed towards a position communicated with the drain opening, and configured to guide a movement of liquid accommodated in the housing, wherein the first groove is formed to have a wider recessed area than the second groove to increase a washing water amount and reduce a backflow of washing water to the drain opening during a circulation process.