The sequence of the acquisition of a correction value of a conveying error depending on the eccentricity of the conveying roller (correction value for eccentricity) and the acquisition of a correction value of a conveying error depending on the outer diameter of the roller (correction value for outer diameter) is considered to acquire a precise correction value for outer diameter. A test pattern to acquire the correction values for eccentricity and for outer diameter is formed with an area exceeds the area corresponding to an integer multiple of the circumferential length of the roller. The correction value for eccentricity and that for outer diameter are acquired in this sequence. The fluctuation in the conveying error is reduced by the application of the correction value for eccentricity, and the influence of the excess area is made smaller before the correction value for outer diameter is acquired by averaging the conveying errors.