An apparatus for treating laundry, comprising: a cabinet including a front panel having an opening; a door configured to be seated on the front panel to open/close the opening, the door having a diameter greater than the opening; a control panel provided to a upper part of the front panel, the control panel including a seating recess formed along a shape of an outer circumference of the door in a bottom part of the control panel and having a upper part of the door seated thereon and a withdraw hole provided beside of the seating recess; a detergent box provided to be withdrawable from the withdraw hole and having a space for accommodating detergent; and a handle panel coupled to a front side of the detergent box; wherein the handle panel has one lateral side surface corresponding to a shape of an outer circumference of the seating recess; the detergent box further includes a coupling panel provided to the front side of the detergent box thereof so as to be coupled to the handle panel; and a preventing part is formed along the lateral side surface of the handle panel and is configured to couple the lateral side surface of the handle panel to the coupling panel to prevent the lateral side surface from being spaced apart from the front side of the detergent box, wherein the preventing part comprises a fastening portion provided to one of the coupling panel and the lateral side surface, and a fixing portion provided to the other one of the coupling panel and the lateral side surface so as to be coupled to the fastening portion, and wherein the fastening portion is attached to the fixing portion with a snap fit connection. a cabinet including a front panel having an opening; a door configured to be seated on the front panel to open/close the opening, the door having a diameter greater than the opening; a control panel provided to a upper part of the front panel, the control panel including a seating recess formed along a shape of an outer circumference of the door in a bottom part of the control panel and having a upper part of the door seated thereon and a withdraw hole provided beside of the seating recess; a detergent box provided to be withdrawable from the withdraw hole and having a space for accommodating detergent; and a handle panel coupled to a front side of the detergent box; wherein the handle panel has one lateral side surface corresponding to a shape of an outer circumference of the seating recess; the detergent box further includes a coupling panel provided to the front side of the detergent box thereof so as to be coupled to the handle panel; and a preventing part is formed along the lateral side surface of the handle panel and is configured to couple the lateral side surface of the handle panel to the coupling panel to prevent the lateral side surface from being spaced apart from the front side of the detergent box, wherein the preventing part comprises a fastening portion provided to one of the coupling panel and the lateral side surface, and a fixing portion provided to the other one of the coupling panel and the lateral side surface so as to be coupled to the fastening portion, and wherein the fastening portion is attached to the fixing portion with a snap fit connection.