PURPOSE: To operate a current-voltage conversion circuit with a low voltage in a simple circuit constitution and to prevent chattering of the output by adding a current hysteresis dependent upon a current mirror circuit.

CONSTITUTION: When an input current IIN rises from 0 to ≥10μA (going path), an output voltage VOUT rises; and when it is equal to a voltage VBE of a transistor TR 3, a current mirror circuit 4 starts the operation. Therefore, the voltage VOUT quickly rises to reach a maximum value, and the displacement point of the voltage VOUT in the going path corresponds to the time when the current IIN is 10μA. In the case of the return path of reduction of the current IIN to 0, a collector current I2 of a TR 2 has a maximum value I2 (15μA) still when the current IIN is 10μA. Consequently, a base current IB does not flow to an output TR 1, and the voltage VOUT does not drop. It starts to drop when the current IIN is reduced to 5μA, and the current I is reduced in accordance with the drop of the voltage VOUT, and the voltage VOUT quickly drops. That is, the displacement point in the return path corresponds to the time when the current IIN is 5μA, and this displacement point is different from that in the going path, and a hysteresis is obtained.