A drain pump assembly, comprising: a pump motor; an impeller including: a hub; an impeller shaft extending from a center of the hub and arranged to connect to a rotation shaft of the pump motor; and a blade extending from an outer circumferential surface of the impeller shaft, wherein the hub is arranged at a proximal end of the impeller shaft; a housing arranged to accommodate the pump motor, wherein the housing includes: an impeller hole through which the impeller passes; defined in a pump motor seat part defined in a bottom part of the housing for the pump motor to be seated thereon; and a discharge port protruding from a point at the bottom part of the housing, which is spaced apart from the pump motor seat part; and a pump case coupled to the housing, the pump case having a suction hole for suctioning water, wherein the suction hole has the same center as that of the impeller shaft, and wherein the pump case comprises a shaft shield part that extends from a portion of an edge of the suction hole to the center of the suction hole to cover a portion of the suction hole and to shield a distal end of the impeller shaft; characterized in that the pump motor seat part is stepped downward from the bottom part of the housing, and the impeller hole is defined inside the pump motor seat part. a pump motor; an impeller including: a hub; an impeller shaft extending from a center of the hub and arranged to connect to a rotation shaft of the pump motor; and a blade extending from an outer circumferential surface of the impeller shaft, wherein the hub is arranged at a proximal end of the impeller shaft; a housing arranged to accommodate the pump motor, wherein the housing includes: an impeller hole through which the impeller passes; defined in a pump motor seat part defined in a bottom part of the housing for the pump motor to be seated thereon; and a discharge port protruding from a point at the bottom part of the housing, which is spaced apart from the pump motor seat part; and a hub; an impeller shaft extending from a center of the hub and arranged to connect to a rotation shaft of the pump motor; and a blade extending from an outer circumferential surface of the impeller shaft, wherein the hub is arranged at a proximal end of the impeller shaft; a housing arranged to accommodate the pump motor, wherein the housing includes: an impeller hole through which the impeller passes; defined in a pump motor seat part defined in a bottom part of the housing for the pump motor to be seated thereon; and a discharge port protruding from a point at the bottom part of the housing, which is spaced apart from the pump motor seat part; and an impeller hole through which the impeller passes; defined in a pump motor seat part defined in a bottom part of the housing for the pump motor to be seated thereon; and a discharge port protruding from a point at the bottom part of the housing, which is spaced apart from the pump motor seat part; and a pump case coupled to the housing, the pump case having a suction hole for suctioning water, wherein the suction hole has the same center as that of the impeller shaft, and wherein the pump case comprises a shaft shield part that extends from a portion of an edge of the suction hole to the center of the suction hole to cover a portion of the suction hole and to shield a distal end of the impeller shaft; characterized in that the pump motor seat part is stepped downward from the bottom part of the housing, and the impeller hole is defined inside the pump motor seat part.