Performed is conveying-error correction in accordance with the kind and the number of rollers that are actually involved in the conveying of a printing medium. Each of the rollers that are potentially involved in the conveying of the printing medium has a unique amount of eccentricity, and may affect the quality of image to be printed in a peculiar manner. To address this problem, a surface of the printing medium is divided into areas according to the number and the combination of the rollers that are actually involved in the conveying. A pattern each is printed for each of the areas thus formed while the pattern enables the detection of the conveying error. A correction value to correct the conveying error is calculated using each of the patterns. The correction values thus obtained are reflected in the conveying of the printing medium.