PURPOSE: To eliminate redundant operation and prevent misoperation by providing a step-back circuit which sends its output to a computer body.

CONSTITUTION: The mouse 1 is equipped with the step-back circuit 8 in addition to a spherical body 2, an association rod 3, a slit disk 4, a photointerrupter 5, and an output part 6. This step-back circuit 8 consists of a reset button, an execution button, a counter, a control part, a step-back waveform generation part, etc. The counter is reset with the reset button and a number set in the counter is set in the step-back waveform generation part as a step-back quantity with the execution button. This step-back waveform generation part sends set-back pulses out to the computer body as many as the set number to reset the counter.