PURPOSE: To reduce the number of components of a key input circuit, by providing forward diodes which transmit a key input signal to a plurality of timing signal lines and data lines in matrix constitution with higher impedance.

CONSTITUTION: TM signal lines TL1WTLn to which a plurality of timing TM signals are applied, and data lines KL1WKL4 of matrix constitution transferring key input signals K1WK4 to a CPU are provided and each data line is grounded via resistors R1WR4. The signals K1WK4 are applied to the signal line TL1 and the data lines KL1WKL4 respectively through diodes D11WD14 and D21WD24. When the signal K1 goes to H level and the signal T1 goes to L level, a current i flows to the signal line TL1 via the D11 and no current i flows to the data line KL1 because the data line KL1 has higher impedance than that of the signal TL1 due to the resistor R1. When the signal T1 goes to H level, since both ends of the D11 is at the same level, no current flows to the D11 and the signal K1 of H level flows to the data line KL1 via the D21.