A mobile terminal, comprising: a display unit configured to display at least a first 3D object at a first 3D depth level and a plurality of second 3D objects at a plurality of second 3D depth levels that are different than the first 3D depth level; and a controller configured to: - receive a first selection action on the first 3D object and a second selection action on the second 3D objects, wherein the first and second selection actions include first and second touch actions of each of the first and second objects, - if the second touch action is input within a certain time after an input of the first touch action, set the first 3D object, which is first touched, to a reference object, and the second 3D objects, which are later touched, to conversion objects, wherein the reference object includes an object which serves as a reference for conversion, and the conversion objects include objects which are subjected to the conversion, - convert the second 3D depth levels of the second 3D objects to match the first 3D depth level of the first 3D object based on the first and second selection actions, and - control the display unit to display the first and second 3D objects at the first 3D depth level. a display unit configured to display at least a first 3D object at a first 3D depth level and a plurality of second 3D objects at a plurality of second 3D depth levels that are different than the first 3D depth level; and a controller configured to: - receive a first selection action on the first 3D object and a second selection action on the second 3D objects, wherein the first and second selection actions include first and second touch actions of each of the first and second objects, - if the second touch action is input within a certain time after an input of the first touch action, set the first 3D object, which is first touched, to a reference object, and the second 3D objects, which are later touched, to conversion objects, wherein the reference object includes an object which serves as a reference for conversion, and the conversion objects include objects which are subjected to the conversion, - convert the second 3D depth levels of the second 3D objects to match the first 3D depth level of the first 3D object based on the first and second selection actions, and - control the display unit to display the first and second 3D objects at the first 3D depth level. - receive a first selection action on the first 3D object and a second selection action on the second 3D objects, wherein the first and second selection actions include first and second touch actions of each of the first and second objects, - if the second touch action is input within a certain time after an input of the first touch action, set the first 3D object, which is first touched, to a reference object, and the second 3D objects, which are later touched, to conversion objects, wherein the reference object includes an object which serves as a reference for conversion, and the conversion objects include objects which are subjected to the conversion, - convert the second 3D depth levels of the second 3D objects to match the first 3D depth level of the first 3D object based on the first and second selection actions, and - control the display unit to display the first and second 3D objects at the first 3D depth level.