PURPOSE: To detect the short-circuit of a switch contact and to attain the operation of all switches even if any of matrix-like switch contacts is turned to a short-circuited state.

CONSTITUTION: This switch matrix input interface circuit is constituted of a switch matrix circuit 17 for outputting external switch input information as contact signals for two-systems and a switch input controller 2 connected to the circuit 17 to receive contact signal information from the circuit 17 and transfer data to/from a CPU 1. The controller 2 integrates a return line 6 capable of inputting contact signals for two systems and a switch status monitoring circuit 8 for detecting the abnormality of the contact signals and has status logic 13 for controlling a line switching circuit 10 based upon an instruction outputted from control logic 4 when one system is abnormal and storing abnormal status information to be read out by the CPU 1.