PURPOSE: To obtain the electric potential difference between two voltages.

CONSTITUTION: Two input voltages V1 and V2 are input to resistance R3 and R4, respectively, and currents I1 and I2 flowing in each resistance R3 and R4 are equalized by a current mirror circuit 1. Early effect taking place in each transistor Q1 and Q2 in the current mirror circuit 1 is eliminated by each of Early effect preventing resistances R1 and R2. With an emitter follower transistor Q3 in an output buffer circuit part 3, the voltage between the base emitters of the transistor Q1 in the current mirror circuit 1 is eliminated, and with a correction circuit part 4, the voltage escalation due to the Early effect prevention resistance R1 is eliminated. And the electric potential difference between the input voltages V1 and V2 is output as an output voltage V0.