Disclosed is a plate-making method and a computer-to-cylinder type lithographic printing method, each of which comprises filtering an oil-based ink; forming an image directly on a plate material by an ink jet process comprising ejecting said filtered oil-based ink using electrostatic field based on signals of image data; and fixing said formed image to prepare a printing plate. A value is determined which corresponds to the braking force set by the drive slip regulation. The security device is attached to the rear panel and covers the connector. A baffle member is deployed downstream of the blower unit at an elevation above the blower unit so as to alter a flow path of ambient air flowing through a discharge path of the blower unit.