There is a known HMD that is worn around a user's head and can present the user with an image in a virtual space with the aid of a display or any other device disposed in front of the user. In particular, the HMD disclosed in Patent Document 1 can display a 360-degree panoramic image in a three-dimensional virtual space. Such an HMD typically includes a variety of sensors (an acceleration sensor and an angular velocity sensor, for example) and measures data on the attitude of an HMD main body. In particular, the direction of the sight line of the eyes looking at the panoramic image can be changed in accordance with information on the angle of rotation of the head. That is, when the user who wears the HMD rotates his/her own head, the direction of the sight line of the eyes looking at the 360-degree panoramic image is changed accordingly, whereby the user's immersive sensation in the video world is enhanced for improvement in entertainment quality (see paragraphs [0004], [0005], [0006], and [Abstract] of Patent Document 1).
Patent Document 1 further discloses that the user's gesture in the form of motion of the head is related in advance to operation (display screen switching, for example) on the screen of the HMD, and when the user's gesture is identified on the basis of the inclination of the head or the acceleration thereof, screen operation related to the gesture is performed. Inconvenience in controller operation resulting from the fact that the user who wears the HMD is unable to see his/her own hands and therearound is therefore solved (see paragraphs [0008] to [0009] in Patent Document 1).