A handle mounting structure includes a handle including a handle shaft with a sliding space defined in one side thereof and a mounting unit located at one end thereof, a locking mechanism including an insert plate slidably inserted into the sliding space and a torsion spring mounted in the sliding space and stopped between the handle and the insert plate to impart a pressure to the insert plate toward the outside of the sliding space, and a positioning device including a flat base pivotally coupled to the handle and a hook block located at a bottom side of the flat base. The handle can be fastened to a sliding box of a cabinet through locking mechanism and the positioning device, so that the handle is not easily separated from the sliding box, and the sliding box can be surely pulled out of or pushed into the cabinet through the handle.