PURPOSE: To obtain a photo functional element which stably operates against the variation in the external environment by providing an amplifying feedback path which feeds back the output of a photodetector for receiving the outputted light of a semiconductor laser having electrodes divided in the axial direction of a resonator to one of electrodes.

CONSTITUTION: A semiconductor laser 1 has the first electrode 2 for injecting a positive current and the second electrode 3 for injecting a constant current smaller than an oscillation threshold value. An active layer 6 is divided into a light amplifying region 7 which has a gain larger than the loss due to sufficient injection of the current and a oversaturation absorbing region 8 which has a loss larger than the gain due to insufficient injection of the current. Part 10 of the outputted light 9 is converted to a photocurrent via a photodetector 12, is amplified through an amplifier 13, and is negatively fed back as a signal current I3 to the second electrode 3. The light output to the injected positive current I1 can be maintained substantially constantly by suitably regulating the value of the photocurrent by the amplifier 13.