PURPOSE: To prevent chattering with simple constitution by delaying a latch signal for setting an encoded output of an input signal from a key contact point to a flip-flop for a longer time than the chattering period of the key contact point.

CONSTITUTION: To an encoder 1, contact point information (a) of information S0WSn from a key contact point S is inputted, and its output (b) encoded in plural bits is applied to a flip-flop 6. To a gate circuit 3, an OR signal of the S0WSn and the output from a clock generating circuit 2 are applied. The output (d) from the gate circuit 3 triggers a monostable multivibrator 4 and with the rise of its output (e) a multivibrator 5 sends a latch signal (f) that is delayed for the time longer than the chattering period to the flip-flop 6. With this process, a buffer gate 7 is capable of receiving information that is not affected by chattering.