A drum type washing machine, comprising: a housing; a spin tub to hold laundry to be washed, whereby the spin tub comprises a cylindrical body; and a ball balancer (20,30) coupled to the spin tub to compensate for a dynamic imbalance during rotation thereof, the ball balancer (20,30) comprising a first housing (22,32) and a second housing (23,33) joined to each other to form an annular-shaped race having a closed internal space (20a,30a) in which a plurality of balls (21,31) and viscous fluid are accommodated, the first housing (22,32) including a first side wall (22a,32a), a second side wall (22b,32b) and a connecting wall (22c,32c) to form a three-sided annular-shaped structure having an open side, and the second housing (23,33) being adapted to cover the open side of the first housing (22,32), the first housing (22, 32) having at least one support (24, 34) for reinforcing a strength of the balancer (20, 30), the at least one support (24,34) protruding from the first housing (22, 32), characterized in that the spin tub rotates with respect to a substantially horizontal axis of the drum type washing machine and comprises a front member and a rear member, the front member having a front wall with an opening formed therein for receiving laundry and with an annular recess corresponding to the balancer (20, 30) such that the balancer (20, 30) is coupled to the spin tub by being fitted within the annular recess, and an outer annular side wall of the annular recess establishes physical contact with a predefined area of an inner surface of the cylindrical body and the at least one support (24,34) comes into contact with the outer annular side wall of the annular recess such that during a rotation of the spin tub the balls contained in the ball balancer (20, 30) are supported in a direction of centrifugal force by the first side wall (22a,32a) of the first housing (22, 32), the at least one support (24, 34), the outer annular side wall of the annular recess and the cylindrical body of the spin tub. a housing; a spin tub to hold laundry to be washed, whereby the spin tub comprises a cylindrical body; and a ball balancer (20,30) coupled to the spin tub to compensate for a dynamic imbalance during rotation thereof, the ball balancer (20,30) comprising a first housing (22,32) and a second housing (23,33) joined to each other to form an annular-shaped race having a closed internal space (20a,30a) in which a plurality of balls (21,31) and viscous fluid are accommodated, the first housing (22,32) including a first side wall (22a,32a), a second side wall (22b,32b) and a connecting wall (22c,32c) to form a three-sided annular-shaped structure having an open side, and the second housing (23,33) being adapted to cover the open side of the first housing (22,32), the first housing (22, 32) having at least one support (24, 34) for reinforcing a strength of the balancer (20, 30), the at least one support (24,34) protruding from the first housing (22, 32), characterized in that the spin tub rotates with respect to a substantially horizontal axis of the drum type washing machine and comprises a front member and a rear member, the front member having a front wall with an opening formed therein for receiving laundry and with an annular recess corresponding to the balancer (20, 30) such that the balancer (20, 30) is coupled to the spin tub by being fitted within the annular recess, and an outer annular side wall of the annular recess establishes physical contact with a predefined area of an inner surface of the cylindrical body and the at least one support (24,34) comes into contact with the outer annular side wall of the annular recess such that during a rotation of the spin tub the balls contained in the ball balancer (20, 30) are supported in a direction of centrifugal force by the first side wall (22a,32a) of the first housing (22, 32), the at least one support (24, 34), the outer annular side wall of the annular recess and the cylindrical body of the spin tub.