An illuminance sensor detects a flicker with higher accuracy than in the related art. The illuminance sensor includes: a light receiving unit that receives light and outputs a current; a flicker measurement counter circuit that performs AD conversion on the current and outputs a first digital signal to a flicker measurement storage device; an illuminance measurement counter circuit that performs AD conversion on the current and outputs a second digital signal to an illuminance measurement storage device; and a flicker detection unit that detects a flicker by analyzing the first digital signal stored in the flicker measurement storage device. A cycle during which the first digital signal is output from the flicker measurement counter circuit is shorter than a cycle during which the second digital signal is output from the illuminance measurement counter circuit.