PURPOSE: To eliminate the need for the lifting movement of a mouse at the time of inputting a large moving amount using the mouse on a small desk and to prevent malfunction.

CONSTITUTION: A movement detection circuit 1 is a circuit for detecting the moving direction of the mouse and the moving amount of a moving distance from the reflection amount of a light beam or the rolling amount of a built-in ball and outputs the digital signal of a fluctuation amount through a masking circuit 4 to a personal computer. Selection switching circuit 2a and 2b are provided with the push button switches of 'dicision' and 'cancellation', convert ON/OFF states into electrical level signals and output them to the masking circuit 4. The masking circuit 4 is provided with relay contact circuits 4a, 4b and 4c, interrupts the digital signals from the movement detection circuit 1 and the electrical level signals from the selection switching circuits 2a and 2b by '1' level signals from an operation invalidation switch 3 and performs masking so that the movement/selection state of the mouse is not outputted to the personal computer of the outside.