A head-mounted device (HMD) for enabling a 3D drawing interaction in a mixed-reality space is provided. The HMD includes a frame section, a rendering unit providing a specified image, a camera unit attached to the frame section to pick up an image for rendering, and a control unit configured to, when the camera unit picks up an image of a specified marker, perform a calibration process based on position information of the image of the marker displayed on a screen of the HMD and to, when there is a motion of an input device for interaction with a virtual whiteboard, obtain position information of an image of the input device displayed on a virtual camera screen based on position information of the whiteboard.