A laundry machine, comprising: a cabinet forming an exterior appearance of the laundry machine; a tub provided inside the cabinet; a drum rotatably provided inside the tub; a balancer housing coupled to a front portion or a back portion of the drum, wherein a plurality of gear teeth is formed along an inner circumferential surface of the balancer housing; and a balancing unit movably formed inside the balancer housing, wherein the balancing unit comprises: a body forming an exterior of the balancing unit, a driving motor generating a driving force, a driving gear rotating by receiving the driving force from the driving motor and interlocking with the gear teeth of the balancer housing, and a controller controlling a rotation speed and a rotation direction of the driving motor, characterized in that the body includes a first cutout section formed on a first horizontal end portion of the body, a first mass body on one lateral side of the first horizontal end portion of the body based upon the first cutout section, and a first wheel on another lateral side of the first horizontal end portion of the body based upon the first cutout section and configured to roll within the balancer housing, wherein an elastic member is provided between the first mass body and the first wheel, so as to push the first mass body and the first wheel to both lateral sides of the body, wherein a hollow second cutout section is formed on a second horizontal end portion of the body, wherein a second mass body is provided on one lateral side of the second horizontal end portion of the body based upon the second cutout section, and wherein the driving motor is provided in the second mass body. a cabinet forming an exterior appearance of the laundry machine; a tub provided inside the cabinet; a drum rotatably provided inside the tub; a balancer housing coupled to a front portion or a back portion of the drum, wherein a plurality of gear teeth is formed along an inner circumferential surface of the balancer housing; and a balancing unit movably formed inside the balancer housing, wherein the balancing unit comprises: a body forming an exterior of the balancing unit, a driving motor generating a driving force, a driving gear rotating by receiving the driving force from the driving motor and interlocking with the gear teeth of the balancer housing, and a controller controlling a rotation speed and a rotation direction of the driving motor, characterized in that the body includes a first cutout section formed on a first horizontal end portion of the body, a first mass body on one lateral side of the first horizontal end portion of the body based upon the first cutout section, and a first wheel on another lateral side of the first horizontal end portion of the body based upon the first cutout section and configured to roll within the balancer housing, wherein an elastic member is provided between the first mass body and the first wheel, so as to push the first mass body and the first wheel to both lateral sides of the body, wherein a hollow second cutout section is formed on a second horizontal end portion of the body, wherein a second mass body is provided on one lateral side of the second horizontal end portion of the body based upon the second cutout section, and wherein the driving motor is provided in the second mass body. a body forming an exterior of the balancing unit, a driving motor generating a driving force, a driving gear rotating by receiving the driving force from the driving motor and interlocking with the gear teeth of the balancer housing, and a controller controlling a rotation speed and a rotation direction of the driving motor, characterized in that the body includes a first cutout section formed on a first horizontal end portion of the body, a first mass body on one lateral side of the first horizontal end portion of the body based upon the first cutout section, and a first wheel on another lateral side of the first horizontal end portion of the body based upon the first cutout section and configured to roll within the balancer housing, wherein an elastic member is provided between the first mass body and the first wheel, so as to push the first mass body and the first wheel to both lateral sides of the body, wherein a hollow second cutout section is formed on a second horizontal end portion of the body, wherein a second mass body is provided on one lateral side of the second horizontal end portion of the body based upon the second cutout section, and wherein the driving motor is provided in the second mass body.