A drum type washing machine, comprising: a housing; a spin tub to hold laundry to be washed, and a ball balancer, having an annular shape, coupled to the spin tub to compensate for a dynamic imbalance during rotation thereof, the ball balancer comprising a first housing and a second housing defining a closed internal space in which a plurality of balls and viscous fluid are accommodated, the first housing having an open side, and the second housing being adapted to cover the open side of the first housing, wherein the first housing includes a first side wall, a second side wall and a third wall wherein the first side wall and the second side wall of the first housing are opposite each other, whereby the spin tub rotates with respect to an axis of the washing machine; characterized in that the first housing and the second housing are fused to each other, and the first housing includes a plurality of supports formed on an outer surface thereof to establish contact with the spin tub, wherein each of the supports protrudes parallel to said first side wall and to said second side wall of the first housing and is disposed at regular intervals along the first and second walls and, ends of the first housing extend from an end of the first side wall and from an end of the second side wall and the supports have a length such that the supports extend from the first housing to contact a wall of an annular recess of the spin tub, so that the first side wall and the second side wall are further increased in strength and additionally function to guide the balancer so as to be maintained in the annular recess in place. a housing; a spin tub to hold laundry to be washed, and a ball balancer, having an annular shape, coupled to the spin tub to compensate for a dynamic imbalance during rotation thereof, the ball balancer comprising a first housing and a second housing defining a closed internal space in which a plurality of balls and viscous fluid are accommodated, the first housing having an open side, and the second housing being adapted to cover the open side of the first housing, wherein the first housing includes a first side wall, a second side wall and a third wall wherein the first side wall and the second side wall of the first housing are opposite each other, whereby the spin tub rotates with respect to an axis of the washing machine; characterized in that the first housing and the second housing are fused to each other, and the first housing includes a plurality of supports formed on an outer surface thereof to establish contact with the spin tub, wherein each of the supports protrudes parallel to said first side wall and to said second side wall of the first housing and is disposed at regular intervals along the first and second walls and, ends of the first housing extend from an end of the first side wall and from an end of the second side wall and the supports have a length such that the supports extend from the first housing to contact a wall of an annular recess of the spin tub, so that the first side wall and the second side wall are further increased in strength and additionally function to guide the balancer so as to be maintained in the annular recess in place.