Patent ID: 7794073

Claim:
An ink jet printer comprising: an ink cartridge including an ink tank for storing ink therein and a recording head for discharging the ink stored in the ink tank to form an image on a recording paper sheet; a cartridge holding member for holding the ink cartridge; a driving means for reciprocating the cartridge holding member in a direction substantially perpendicular to a conveying direction of the recording paper sheet; a printing shear detection sensor including a light emitting device which emits light toward the recording paper sheet and a light receiving device which receives the light emitted from the light emitting device and reflected on the recording paper sheet, for reading a predetermined printing shear detection pattern formed on the recording paper sheet by the recording head; and a printing shear correction control means for correcting printing shear by adjusting discharge timing of the recording head based on the printing shear detection pattern read by the printing shear detection sensor, wherein the printing shear detection sensor further has a light guide, which is a single element and other than a condensing lens, disposed on an optical path of the light emitted from the light emitting device and has a cross section with substantially uniform width in the conveying direction of the recording paper sheet, and has a cross section so as to condense the light emitted from the light emitting device on the recording paper sheet in the direction substantially perpendicular to the conveying direction of the recording paper sheet; and thereby the light emitted from the light emitting device is incident on the light guide from above, emitted toward the recording paper sheet from the bottom of the light guide and projected on the recording paper sheet substantially in a shape of a slit.