Abstract: A check system for a control board having a microcomputer includes a checker which is actuated by a check program provided with the microcomputer. At each time line shift signals are generated, all input signal levels of the respective input connectors of the control board, except for the given connector, are detected to output at check output connectors signal levels corresponding to the input signal levels in the input line check. The respective output connectors of the control board, except for the certain connector, are rendered in active states, in sequence, in an output line check. The system thus detects an abnormal state disposed between the terminals of the microcomputer and the connectors of the control board.