An optical sensor includes a semiconductor layer including a first region, a second region, and a third region between the first region and the second region, a first electrode, a photoelectric conversion layer between the third region and the first electrode, and voltage supply circuitry applying a voltage between the first electrode and the first region to apply a bias voltage to the photoelectric conversion layer. The photoelectric conversion layer has a characteristic showing how a density of current flowing through the photoelectric conversion layer varies with the bias voltage applied to the photoelectric conversion layer. The characteristic includes a third voltage range where an absolute value of a rate of change of the current density relative to the bias voltage is less than in a first voltage range and a second voltage range, the third voltage range being between the first voltage range and the second voltage range.