PURPOSE: To provide a translucent source document projector which does not become the hindrance to the placing of a source document in the case of reading a large-sized source document.

CONSTITUTION: A projection unit 2 is displaced with respect to a source document reader body, and selectively occupies a projecting position to radiate a luminous flux for forming the image of the translucent source document by such displacement with respect to the source document reader body and a housing position to house the projection unit in the source document reader body. When the unit 2 is housed at the housing position, the partial surface of the housing of the unit 2 becomes nearly the same as a source document placing surface 51.