PURPOSE: To facilitate the detection of an input fault of a decoder circuit by adding a circuit applying abnormality discrimination depending on a current sensing between a test signal line and a reference signal line.

CONSTITUTION: The titled circuit consists of a test signal line 490 connecting to N-channel transistors(NCH-TR) 405.415...475 turned on when outputs of inverters 400.410...470 go to '1', NCH-TR 800∼807, a reference signal line 890 connected to the NCH-TRs 800∼807, a known current sense amplifier (sense amplifier) 700 sensing a current flowing to the test signal line 490 and the reference signal line 890, an output signal line 900 of the sense amplifier 700, a power supply line 600 of each circuit and a ground line 650. The impedance between the circuit connected with plural TRs in parallel and the reference circuit is compared to output a comparison signal. Thus, a fault of the decoder output is detected easily.