1. An image reading apparatus comprising at least one laser stimulating ray source, a stage on which two or more kinds of image carriers can selectively be placed, a scanning mechanism for scanning the image carrier with a laser beam emitted from the at least one laser stimulating ray source, thereby stimulating the image carrier, a light detector for photoelectrically detecting light emitted from the image carrier in response to stimulation by the laser beam and a confocal optical system for leading light emitted from the image carrier to the light detector, the image reading apparatus further comprising a confocal switching means having diameter-variable pinhole means and disposed between the confocal optical system and the light detector and whose pinhole diameter is variable.