A pressure sensor comprises a sensor diaphragm which on one of its surfaces can be acted upon by the fluid pressure to be defected. At least one of the first, second, and third lens group has an aspherical surface. A cascode current source unit includes a plurality of cascode current sources connected in parallel. In yet another embodiment, guard areas are provided in a tip portion and a back end portion of the data area. When the image is formed onto the sheet, a side edge of the sheet on the side which is come into contact with the aligning plate on the side fixed as a reference wall upon aligning is used as a reference and the image is formed.