PURPOSE: To achieve a higher diagnosis rate, by changing over a switching means by a control signal for specifying the diagnosis mode and the normal mode to selectively output the latch means output and the flipflop output according to the mode.

CONSTITUTION: A selector control signal 30' is at the level '0' in the diagnosis mode, where two switches in a selector are both turned to the position (a). Consequently, the diagnosis data Q0 and -Q0 are outputted as signals Q1 and -Q1 through the selector 100 after transferred to an SF section 55 at the timing of C2='1' level. In the reading operation of the diagnosis data, the signal -Q1 is outputted to a diagnosis bus line 17-1 through a switch 53 and in the normal mode, the selector control signal 30' moves to the '1' level, making both the switches in the selector turn to the position (b). The outputs Q0 and -Q0 of an MF section are outputted as signals Q1 and -Q1 and to increase the delay time with an addition circuit with diagnosis, no other than the delay time of the selector 100 need to be considered thereby enabling a higher speed. This facilitates the diagnosing thereby achieving a lower cost and a higher reliability.