Patent ID: 7448743

Claim:
An ink jet printer for printing an image on a paper, comprising: a printing head for ejecting ink to print an image on a paper; a cradle for holding the printing head; a print misalignment detection sensor comprising a light-emitting element for irradiating light onto the paper and a light-receiving element for receiving reflection light from the paper so as detect misalignment of an image printed on the paper; and a support member for supporting the light-emitting element and the light-receiving element and for being mounted on a side surface of the cradle, wherein: the support member comprises (i) a light transmitting groove having a substantially U-shaped cross section to form a light transmitting path of light emitted from the light-emitting element, (ii) a light receiving groove having a substantially U-shaped cross section to form a light receiving path to the light-receiving element, and (iii) an opening on a cradle-mounting side thereof; the cradle comprises a rib being provided on and projected from the side surface thereof to mount the support member, and being inserted into the light transmitting groove and/or the light receiving groove, and further having a semicircular recess at an end thereof; and the semicircular recess of the rib inserted into the light transmitting groove and/or the light receiving groove causes the light transmitting path and/or the light receiving path at the insertion position to have a round shape as seen in cross-sectional view.