A medium detection apparatus is provided with: a light emitting section adapted to emit light; a light receiving section adapted to detect reflected light and output an output value in accordance with an amount of the reflected light; a medium supporting section adapted to support a medium and having a diffusing section adapted to diffuse the light emitted from the light emitting section; and a controller adapted to detect an edge of the medium based on a difference between the output value of the light receiving section when the light receiving section detects light reflected from the medium and the output value of the light receiving section when the light receiving section detects light reflected from the medium supporting section.