In a printer, a sheet discharge port for discharging a sheet therefrom is provided on the upper surface of an exterior case, and a recess portion for preventing invasion of a foreign material into the sheet discharge port is formed in the neighborhood of the sheet discharge port. The recess portion passes by the sheet discharge port, and at least one of the ends thereof is opened to the side surface of the exterior case. The side surface of the exterior case to which the open end of the recess portion is adjacent forms a foreign material discharging passage along which a foreign material discharged from the open end of the recess portion falls down without invading the printer.