PURPOSE: To attain stable circuit operation by providing a means detecting it that all signal lines go to H (all H) and a means letting an output of a latch-up circuit be an L level when all H is first detected by the detection means after application of power source and keeping the L state so as to shorten voltage level uncertainly time at the time of application of power source.

CONSTITUTION: Just after application of power source, since a signal at a point A produced by a resistor Rr, Cr and a Schmitt buffer 5 remains at an L level, the signal at the point A is inputted to a CLR of a D flip-flop 6 to let an output (signal at a point C) of the flip-flop 6 go to H and output levels of D0'-Dn' (signal input terminal 3) all go to H via an OR circuit 4. That is, just after application of power source, the level of the data buses D0'-Dn' is set to H. When the signal at the point A and the signals of D0-Dn all go to H, a signal at a point C goes to an L level. Thus, the signal levels of the D0-Dn go to the signal levels of the D0'-Dn' (signal input terminal 3) as they are.