A head mounted display comprising: a camera unit configured to detect a first marker and a second marker; a display unit configured to display an augmented reality image (21, 32, 42, 44, 52) corresponding to the first marker or the second marker; and a controller configured to control the camera unit and the display unit, wherein the controller is further configured to: detect at least a part of a 3-dimensional printer as the first marker through the camera unit, display a first augmented reality image of a shape of a 3-dimensional object based on the detected first marker before the 3D object is output by the 3D printer, detect at least a part of the 3D object, which is output from the 3D printer, as the second marker if the 3D printer starts to output the 3D object, update the first augmented reality image to a second augmented reality image based on the first marker and the second marker, display the second augmented reality image and display a control interface for the 3D printer together with the first augmented reality image or the second augmented reality image, characterized in that the processor of the HMD is further configured to: detect an output tray of the 3D printer as the first marker, display the shape of the 3D object at a first location, which is the location of the output tray in a standby state before 3D printing starts, when the output tray of the 3D printer is moved to the outside, and change the location of the augmented reality image from the first location to a second location, which is the location of the output tray moved to the inside of the 3D printer, so that the augmented reality image may be displayed on the output tray moved to the inside of the 3D printer. a camera unit configured to detect a first marker and a second marker; a display unit configured to display an augmented reality image (21, 32, 42, 44, 52) corresponding to the first marker or the second marker; and a controller configured to control the camera unit and the display unit, wherein the controller is further configured to: detect at least a part of a 3-dimensional printer as the first marker through the camera unit, display a first augmented reality image of a shape of a 3-dimensional object based on the detected first marker before the 3D object is output by the 3D printer, detect at least a part of the 3D object, which is output from the 3D printer, as the second marker if the 3D printer starts to output the 3D object, update the first augmented reality image to a second augmented reality image based on the first marker and the second marker, display the second augmented reality image and display a control interface for the 3D printer together with the first augmented reality image or the second augmented reality image, characterized in that the processor of the HMD is further configured to: detect an output tray of the 3D printer as the first marker, display the shape of the 3D object at a first location, which is the location of the output tray in a standby state before 3D printing starts, when the output tray of the 3D printer is moved to the outside, and change the location of the augmented reality image from the first location to a second location, which is the location of the output tray moved to the inside of the 3D printer, so that the augmented reality image may be displayed on the output tray moved to the inside of the 3D printer. detect at least a part of a 3-dimensional printer as the first marker through the camera unit, display a first augmented reality image of a shape of a 3-dimensional object based on the detected first marker before the 3D object is output by the 3D printer, detect at least a part of the 3D object, which is output from the 3D printer, as the second marker if the 3D printer starts to output the 3D object, update the first augmented reality image to a second augmented reality image based on the first marker and the second marker, display the second augmented reality image and display a control interface for the 3D printer together with the first augmented reality image or the second augmented reality image, characterized in that the processor of the HMD is further configured to: detect an output tray of the 3D printer as the first marker, display the shape of the 3D object at a first location, which is the location of the output tray in a standby state before 3D printing starts, when the output tray of the 3D printer is moved to the outside, and change the location of the augmented reality image from the first location to a second location, which is the location of the output tray moved to the inside of the 3D printer, so that the augmented reality image may be displayed on the output tray moved to the inside of the 3D printer. detect an output tray of the 3D printer as the first marker, display the shape of the 3D object at a first location, which is the location of the output tray in a standby state before 3D printing starts, when the output tray of the 3D printer is moved to the outside, and change the location of the augmented reality image from the first location to a second location, which is the location of the output tray moved to the inside of the 3D printer, so that the augmented reality image may be displayed on the output tray moved to the inside of the 3D printer.