A head-mounted display (HMD: 100) in communication with a mobile terminal, the HMD comprising: a display configured to selectively reproduce content; a sensor configured to sense a state in which the HMD is worn by a user; and a controller configured to: present, on the display, notification information about an event detected by the mobile terminal, when the sensor senses a change in the state in which the HMD is worn by the user while the notification information is being presented by the display, control the reproduction state of the content differently according to the changed state in which the HMD is worn by the user, wherein the sensor includes: a proximity sensor configured to sense whether the user's head is adjacent to the HMD, and an eye tracking sensor configured to detect whether the user's eyes can be tracked, wherein the controller is further configured to: determine that the HMD has been completely taken off when the proximity sensor senses that the user's head is not adjacent to the HMD, determine that the HMD has been temporarily taken off when the proximity sensor senses that the user's head is adjacent to the HMD and the eye tracking sensor detects that the user's eyes cannot be tracked, when the HMD has been temporarily taken off while the notification information is being displayed, direct the display to pause the reproducing of the content, and if the user wears the HMD again while the HMD has been temporarily taken off, the pause content is reproduced again; and when the HMD has been completely taken off, direct the display to stop reproducing the content and generate a bookmark information identifying the content and a point in time when the sensor senses the change in the state in which the HMD is worn by the user. a display configured to selectively reproduce content; a sensor configured to sense a state in which the HMD is worn by a user; and a controller configured to: present, on the display, notification information about an event detected by the mobile terminal, when the sensor senses a change in the state in which the HMD is worn by the user while the notification information is being presented by the display, control the reproduction state of the content differently according to the changed state in which the HMD is worn by the user, present, on the display, notification information about an event detected by the mobile terminal, when the sensor senses a change in the state in which the HMD is worn by the user while the notification information is being presented by the display, control the reproduction state of the content differently according to the changed state in which the HMD is worn by the user, wherein the sensor includes: a proximity sensor configured to sense whether the user's head is adjacent to the HMD, and an eye tracking sensor configured to detect whether the user's eyes can be tracked, a proximity sensor configured to sense whether the user's head is adjacent to the HMD, and an eye tracking sensor configured to detect whether the user's eyes can be tracked, wherein the controller is further configured to: determine that the HMD has been completely taken off when the proximity sensor senses that the user's head is not adjacent to the HMD, determine that the HMD has been temporarily taken off when the proximity sensor senses that the user's head is adjacent to the HMD and the eye tracking sensor detects that the user's eyes cannot be tracked, when the HMD has been temporarily taken off while the notification information is being displayed, direct the display to pause the reproducing of the content, and if the user wears the HMD again while the HMD has been temporarily taken off, the pause content is reproduced again; and when the HMD has been completely taken off, direct the display to stop reproducing the content and generate a bookmark information identifying the content and a point in time when the sensor senses the change in the state in which the HMD is worn by the user. determine that the HMD has been completely taken off when the proximity sensor senses that the user's head is not adjacent to the HMD, determine that the HMD has been temporarily taken off when the proximity sensor senses that the user's head is adjacent to the HMD and the eye tracking sensor detects that the user's eyes cannot be tracked, when the HMD has been temporarily taken off while the notification information is being displayed, direct the display to pause the reproducing of the content, and if the user wears the HMD again while the HMD has been temporarily taken off, the pause content is reproduced again; and when the HMD has been completely taken off, direct the display to stop reproducing the content and generate a bookmark information identifying the content and a point in time when the sensor senses the change in the state in which the HMD is worn by the user.