PURPOSE: To improve the operativity of a key input device with conductive rubber contacts, metallic contacts, or the like that provides fast, light key touch input, by detecting and judging a make shorter than a monitor time as a bounce.

CONSTITUTION: During a key read, input key discriminating circuit 23 reads a key signal by timer 29 at any time; when a key signal is turned off owing to a bounce, the off time is counted by monitoring circuit 28, which when the count value is less than a certain value, judges that as a bounce. On the other hand, when the off-time is longer than a certain time, that is considered to be caused by the key input. Since the normal bounce time is 10W20ms and the time interval of the repetitive depression of keys is about 100ms, they can be distinguished. For this purpose, the ≤30ms off-time is set as a bounce to monitoring circuit 28, so that an influence of the bounce can be eliminated.