A conveyed object detector includes first and second image obtaining units disposed at first and second positions different in a conveyance direction, to image a conveyed object to obtain first and second image data; respectively; a recognition unit to recognize an object adhering to the first and second image obtaining units based on imaging at the first and second positions to generate first and second stain data, respectively; a removal unit to remove the first and second stain data from the first and second image data, respectively; and a calculator to generate at least one of a position, a movement amount, and a moving speed of the conveyed object based on first and second corrected image data. Each of the first and second image obtaining units include a light source, an area sensor, and an optical element disposed between the area sensor and the conveyed object.