To provide a printer restraining, to the minimum, productivity from getting worse when one part of drawing pixels gets defective, without increasing an unnecessary cost in a normal operation device, and without shortening a product life.
Performance is maintained by a compensation means for the defective pixel of a plurality of lasers/array lasers, and by reducing a space between paper sheets. This manner is effective, in particular, in a subordinate type of a type of printer in a line of carrying out series development by regulating the space between paper sheets. A process coefficient is not required to be re-regulated by making a conveying speed slow by a speed corresponding to a defective portion, and development manhours are reduced also.