A sheet identification device includes plural detecting units, an estimating unit, and an output unit. The plural detecting units are provided along a transport path along which a sheet is transported by a transport unit, and detect passing of the sheet. The estimating unit estimates a length in a transport direction of the sheet as a detection target on the basis of individual detection results generated by the plural detecting units. The output unit outputs, if the length estimated by the estimating unit on the basis of at least one of the detection results is not a predetermined length, a signal indicating that a sheet having a length in the transport direction different from the predetermined length is being transported.