A 3-dimentional, 3D, display device comprising: a 3D display unit; a measurement unit configured to obtain location information indicating a location of a user located in front of the 3D display unit; and a processor configured to control the 3D display unit and the measurement unit, wherein the processor is further configured to: obtain a first angle, which is a horizontal angle between the 3D display unit and the user, by using the location information, maintain an image displayed on the 3D display unit if the first angle is within a preset first angle range, the preset first angle range corresponding to an optimized or a maximum angle range between the user and the 3D display device, which allows the user to recognize depth of the image, and rotate the image displayed on the 3D display unit based on a vertical axis of the image and in a left or right direction according to the first angle if the first angle departs from the preset first angle range, characterized in that if the first angle is changed and departs from the preset first angle range, the processor is configured to rotate the image displayed on the 3D display unit based on the vertical axis of the image and in an opposite direction of a change direction of the first angle according to the change of the first angle, such that the user is caused inconvenience in viewing the image. a 3D display unit; a measurement unit configured to obtain location information indicating a location of a user located in front of the 3D display unit; and a processor configured to control the 3D display unit and the measurement unit, wherein the processor is further configured to: obtain a first angle, which is a horizontal angle between the 3D display unit and the user, by using the location information, maintain an image displayed on the 3D display unit if the first angle is within a preset first angle range, the preset first angle range corresponding to an optimized or a maximum angle range between the user and the 3D display device, which allows the user to recognize depth of the image, and rotate the image displayed on the 3D display unit based on a vertical axis of the image and in a left or right direction according to the first angle if the first angle departs from the preset first angle range, characterized in that if the first angle is changed and departs from the preset first angle range, the processor is configured to rotate the image displayed on the 3D display unit based on the vertical axis of the image and in an opposite direction of a change direction of the first angle according to the change of the first angle, such that the user is caused inconvenience in viewing the image. obtain a first angle, which is a horizontal angle between the 3D display unit and the user, by using the location information, maintain an image displayed on the 3D display unit if the first angle is within a preset first angle range, the preset first angle range corresponding to an optimized or a maximum angle range between the user and the 3D display device, which allows the user to recognize depth of the image, and rotate the image displayed on the 3D display unit based on a vertical axis of the image and in a left or right direction according to the first angle if the first angle departs from the preset first angle range, characterized in that if the first angle is changed and departs from the preset first angle range, the processor is configured to rotate the image displayed on the 3D display unit based on the vertical axis of the image and in an opposite direction of a change direction of the first angle according to the change of the first angle, such that the user is caused inconvenience in viewing the image.