PURPOSE: To improve the workability for mouse operation by constituting a mouse so that the extent of relative movement outputted from the mouse coincides with an actually calculated extent of relative movement.

CONSTITUTION: A mouse main body 3 consists of an arithmetic unit 1, a direction correcting device 8 consisting of a direction detector 2, a ball 9 rotated in accordance with the mouse main body 3, and encoders 11 and 12 which detect the rotation or the ball 9. The arithmetic unit 1 measures the motion of the ball 9 by encoders 11 and 12 and outputs the direction of the mouse to the direction detector 2 at the time of judging that it is moved by a certain distance, and the distance in the direction where the mouse main body 3 is absolutely moved is calculated based on them and is outputted to a computer.