Abstract: In an image forming apparatus, in a case of duplex printing, a sheet is transported toward an image forming device along a sheet transport route, the image forming device forms an image on a first face, which is one of faces of the sheet, a reverse transport device reverses the front and back faces of the sheet and transports the sheet to a position upstream of a show-through reading device in a sheet transport direction, and the show-through reading device reads a second face, which is another face of the sheet. Then the show-through detector decides whether a show-through has occurred, on a basis of the image that has been read.

Abstract: A first pair of optical fibers are held and fixed to a supporting member in a cantilever form, and oppositely connected to a second pair of the optical fibers that are fixed to a square hole of the alignment material. A magnetic body is adhered to each of the first pair of optical fibers. Around the magnetic bodies, there are aligned hollow solenoid coils, and one pair or two pairs of permanent magnets respectively are oppositely aligned so as to have opposite polarities to each other.