PURPOSE: To prevent malfunction by detecting the condition that trouble occurs in the constitution corresponding to a key and that an effective signal is output by mistake from the key switch, concerning the key switch output abnormality detection circuit which detects the abnormality of the key switch.

CONSTITUTION: This is constituted to have an X row double press detection means 2, which detects that effective signals are output from two or more signal lines of a plurality of X rows of a key switch, a Y row double press detection means 3, which detects that effective signals are output from two or more signal lines of a plurality of Y rows, and an alarm generation means 4, which generates an alarm if either of these detects that effective signals are output from two or more signal lines.