Patent ID: 8780367

Claim:
A detecting device comprising: a detecting unit configured to detect an image on a medium transported in a transport path, wherein the detecting unit includes: a light emitter configured to emit light toward the transport path in which the medium is transported, a light receiver configured to receive reflected light of the light emitted from the light emitter, and a light adjusting portion that is on a path of the reflected light between the light emitter and the light receiver and is configured to rotate, in response to an amount of the emitted light changing, in order to adjust a quantity of the reflected light that is focused onto the light receiver, wherein the light adjusting portion includes: a first wall configured to block a light beam from a first side in a direction substantially orthogonal to a traveling direction of the reflected light, a second wall that is provided at a position separated from the first wall by a certain distance in the traveling direction of the reflected light and that is configured to block the light beam from a second side in the direction substantially orthogonal to the traveling direction of the reflected light, and a rotary shaft that is provided at a midpoint of a line connecting an edge of the first wall adjacent to the traveling direction of the reflected light beam and an edge of the second wall adjacent to the traveling direction of the reflected light beam and that is configured to rotate the first wall and the second wall about the midpoint.