PURPOSE: To switch the gain, or divide a signal of the optical currents in a photoelectric conversion element without affecting the other characteristics.

CONSTITUTION: The sum of currents running through a photoelectric conversion element 5 and a constant current source 7 is introduced to a current mirror circuit 20 as reference currents, and current-amplified by only (Q2 emitter size/Q 1 emitter size) times. When the potential of a gain control terminal 4 is sufficiently lower than the mid-point potential of resistors R1 and R2, a transistor Q5 is turned off, and output currents from an output terminal 3 are only the correcter currents of the transistor Q2. On the other hand, when the potential of the gain control terminal 4 is sufficiently higher than the mid-point potential, the transistor Q5 is turned on, and the output currents from the output terminal 3 flow also to a transistor Q3. Therefore, the gain of the current mirror circuit 20 is changed to (the sum of the emitter size of the Q2 and Q3/Q1 emitter size).