A sheet transport device includes an abutment member that moves downstream in a sheet transport direction and against which a leading end of a sheet that has been transported from upstream in the sheet transport direction abuts; and a transport unit that transports the sheet whose leading end has abutted against the abutment member further downstream. The abutment member moves at least to the transport unit in a state in which the leading end of the sheet abuts against the abutment member, and the abutment member is separated from the leading end of the sheet after the transport unit has started to transport the sheet.