Image forming apparatus and optical sensor detecting target formed on image carrier or recording medium

An image forming apparatus comprising:

• a light-emitting unit configured to emit light toward an image carrier or a recording medium;
• a first light-receiving unit that includes a plurality of light-receiving elements arranged along a first direction that is a movement direction of a target formed on the image carrier or the recording medium, and is arranged so as to receive light emitted from the light-emitting unit and specularly reflected off the image carrier or the recording medium;
• a aperture stop member configured to limit a size of diffused reflection light that is incident on the first light-receiving unit in the first direction;
• a selection unit configured to select whether or not each of the plurality of light-receiving elements in the first light-receiving unit is a first effective light-receiving element;
• a generation unit configured to generate a first detection signal from an output of the first effective light-receiving element selected by the selection unit;
• and
• a detection unit configured to detect a target formed on the image carrier or the recording medium based on the first detection signal.