A head-mounted display for blocking out an outside world from a user's vision when worn by the user to present a video, the head-mounted display comprising: an outside world measurement section, constituted by a camera, which is adapted to measure outside world information; a position measurement section, constituted by an accelerometer and a gyroscope, which is adapted to measure whether a position of the head-mounted display in space changes; a notification information detection section adapted to detect whether or not the information measured by the outside world measurement section indicates the presence of a still object and to detect the distance to the still object based either on the video captured by the camera when the position measurement section detects that the position of the head-mounted display in space has not changed, or on the measurements of the accelerometer and the gyroscope of the position measurement section when the position measurement section detects that the position of the head-mounted display in space has changed; and a notification section adapted to notify the user when the notification information detection section detects presence of a still object at a distance shorter than a given reference distance, wherein the notification section acquires the distance between the position of the head-mounted display and the still object based on the position of the head-mounted display detected by the position measurement section by making use of a reference point for position measurement determined before the movement of the head mounted display, and the position measurement section is configured to set the reference point on the still object by starting measurement of position changes while the head mounted display is located at the reference point and to calculate the distance between the position of the head-mounted display and the still object by integrating position changes with respect to the reference point on the still object. an outside world measurement section, constituted by a camera, which is adapted to measure outside world information; a position measurement section, constituted by an accelerometer and a gyroscope, which is adapted to measure whether a position of the head-mounted display in space changes; a notification information detection section adapted to detect whether or not the information measured by the outside world measurement section indicates the presence of a still object and to detect the distance to the still object based either on the video captured by the camera when the position measurement section detects that the position of the head-mounted display in space has not changed, or on the measurements of the accelerometer and the gyroscope of the position measurement section when the position measurement section detects that the position of the head-mounted display in space has changed; and a notification section adapted to notify the user when the notification information detection section detects presence of a still object at a distance shorter than a given reference distance, wherein the notification section acquires the distance between the position of the head-mounted display and the still object based on the position of the head-mounted display detected by the position measurement section by making use of a reference point for position measurement determined before the movement of the head mounted display, and the position measurement section is configured to set the reference point on the still object by starting measurement of position changes while the head mounted display is located at the reference point and to calculate the distance between the position of the head-mounted display and the still object by integrating position changes with respect to the reference point on the still object.