SHEET TRANSPORT APPARATUS, DOCUMENT READING APPARATUS, AND IMAGE FORMING APPARATUS

One embodiment of a sheet transport apparatus is provided with a sheet transport path for transporting a sheet in a predetermined transport direction, a reflective type optical sensor in which light irradiated from a light-emitting portion to a transported sheet is reflected and reflected light from the sheet is received by a light-receiving portion to detect a presence/absence of the sheet, an irradiated light adjustment portion that adjusts a light amount of the light-emitting portion, a non-image region locating portion that detects an image state on a sheet to locate a non-image region of the sheet, and a control portion that adjusts the light amount of the light-emitting portion by controlling the irradiated light adjustment portion based on a measured value on the non-image region located by the non-image region locating portion.