A write device includes an opening arranged on a casing of a write unit that emits irradiation light to expose a photoreceptor; a shutter unit movably mounted on the casing to open and close the opening; plural wall-like sections having respective different widths and being arranged in a standing manner on a side intersecting with a rotary shaft of a rotator that moves the shutter unit; a detecting unit that detects the plural wall-like sections moving in accordance with the rotation of the rotator; a measuring unit that measures a time period from when a wall-like section is detected until when the wall-like section is no longer detected; and a position detecting unit that determines the detected wall-like section by using the measured time period and the width thereof and detects the position of the shutter unit by using the determined wall-like section.