Image forming apparatus and control method thereof

An image forming apparatus of the invention conveys paper fed by a paper feeding mechanism piece by piece to a paper discharging unit through a paper conveying path. An image forming unit is arranged in a midway portion of this paper conveying path and executes an image forming process for printing an image based on image data on paper being conveyed. A sensor that detects a type of the paper conveyed is arranged on an upstream side with respect to the image forming unit on the paper conveying path. Image forming process conditions for the image forming unit are set in accordance with a detection result of the sensor. When the paper fed to the paper conveying path is paper not detected by the sensor, the image forming process is started awaiting a detection result by the sensor. On the other hand, when the paper is detected by the sensor, the image forming process is started without awaiting paper type detection. Moreover, paper being conveyed is conveyed to the image forming unit, in which the image forming process is started, in synchronization with a printing operation of the image forming unit.