PURPOSE: To remarkably increase the operation speed, by making the reverse break down voltage of diodes constituting a diode logic circuit less than the power supply voltage.

CONSTITUTION: When either one of input signals A∼C is at low level, a transistor Q1 is cut off, and the output is changed to high level of the power supply voltage Vcc. But, since the break down voltage of the diode D1' at the next stage is set around 1 volt, the output high level is clamped to around 1.8V with the base emitter voltage of the transistor Q1' of the next stage and the break down voltage of the diode D1'. Thus, when all the input signals A∼C are at high level, the transistor Q1 is ON and when the output is changed to low level, the inverting speed is made faster since the output amplitude to be changed is smaller.