To make an input device including a gyroscope small in size and light in weight and to improve operability by providing the input device for inputting information controlling a main body device with an optical gyroscope for detecting angular velocity in the directions of one or more axes and a control circuit for processing a signal from the optical gyroscope.

An observation object M is, for instance, a monitor of a computer, etc. The image analysis circuit 32 of a head mount display(HMD) calculates which part of the object M an observer 101 watches carefully by comparing the direction of the object M with respect to the optical axis of an image forming lens system 28 which is obtained by an operation with the direction of the sight line of the observer 101 with respect to the optical axis of the system 28 which is calculated by sight line detection. The direction change of the HMD is also detected by using a direction detecting means 40 such as a gyroscope. Here, a small-sized optical gyroscope is used as the means 40. Then, it is possible to make the HMD small-sized and light in weight even though the small-sized optical gyroscope is mounted on the HMD.