A drum washing machine, comprising: a spin tub to hold laundry to be washed, wherein the spin tub rotating with respect to a horizontal axis of the drum washing machine, and a ball balancer (30, 40) to compensate for a dynamic imbalance during rotation thereof, the ball balancer (30, 40) comprising a first housing (32, 42) having an open side, first and second walls (32a, 32b) facing each other and a third wall connecting the first and second walls (32a, 32b), wherein the first wall is more distant from a center of rotation of the ball balancer (30, 40) than the second wall; a second housing (33, 43) to cover the open side of the first housing (32, 42), wherein the first and second housing (32, 33, 42, 43) are joined together to form an annular shaped space (30a, 40a), and a plurality of balls (31, 41) movably disposed in the annular shaped space (30a, 40a), characterized in that the second housing comprises a fusion groove formed therein so as to correspond to a fusion ridge formed on the first housing so as to enable the fusion ridge to be fitted into the fusion groove when the first housing and the second housing are fused together, wherein the second housing further comprises an outer pocket flange protruding to the first housing on outer sides of the fusion groove so as to be spaced apart from the fusion ridge by a predetermined distance forming an outer pocket therebetween, the outer pocket capable of collecting fusion scraps generated during fusion, and the spin tub has an annular recess, wherein the balancer (30, 40) is installed in the annular recess of the spin tub, and wherein a plurality of supports for reinforcing a strength of the ball balancer (30, 40) are disposed parallel on the outer surface of the first housing along at least the first wall thereof at regular intervals to contact a wall of the recess of the spin tub. a spin tub to hold laundry to be washed, wherein the spin tub rotating with respect to a horizontal axis of the drum washing machine, and a ball balancer (30, 40) to compensate for a dynamic imbalance during rotation thereof, the ball balancer (30, 40) comprising a first housing (32, 42) having an open side, first and second walls (32a, 32b) facing each other and a third wall connecting the first and second walls (32a, 32b), wherein the first wall is more distant from a center of rotation of the ball balancer (30, 40) than the second wall; a second housing (33, 43) to cover the open side of the first housing (32, 42), wherein the first and second housing (32, 33, 42, 43) are joined together to form an annular shaped space (30a, 40a), and a plurality of balls (31, 41) movably disposed in the annular shaped space (30a, 40a), characterized in that the second housing comprises a fusion groove formed therein so as to correspond to a fusion ridge formed on the first housing so as to enable the fusion ridge to be fitted into the fusion groove when the first housing and the second housing are fused together, wherein the second housing further comprises an outer pocket flange protruding to the first housing on outer sides of the fusion groove so as to be spaced apart from the fusion ridge by a predetermined distance forming an outer pocket therebetween, the outer pocket capable of collecting fusion scraps generated during fusion, and the spin tub has an annular recess, wherein the balancer (30, 40) is installed in the annular recess of the spin tub, and wherein a plurality of supports for reinforcing a strength of the ball balancer (30, 40) are disposed parallel on the outer surface of the first housing along at least the first wall thereof at regular intervals to contact a wall of the recess of the spin tub.