A color registration error detecting method for repeatedly forming a plurality of registration error detection patterns of different colors on an image carrier, detecting the registration error detection patterns, and detecting a color registration error from detection signals of the patterns. In this method, a sampling length and a sampling frequency for detection of the registration error detection patterns are set so as to satisfy the conditions of (1) the sampling length is to be approximated to a wavelength of a vibrational component be read with a registration error component by registration error detecting means or to an integer multiple of the wavelength; (2) the sampling length is to be set as large as possible; and (3) the sampling frequency and an integer multiple thereof are to be separated as far as possible from a frequency of the vibrational component. Accordingly, the detection accuracy of the color registration error can be improved by sampling the original color registration error only from the color image registration error and the various vibrational components to be read by the pattern detecting means, thereby realizing both a high quality and a high speed in a color image forming device.
Color registration error detecting method