A color image forming apparatus comprising: image forming means for forming misregistration detection patterns; a transfer member on which the misregistration detection patterns are transferred; first detection means and second detection means (6L, 6R) arranged to be juxtaposed in a direction perpendicular to a moving direction of said transfer member; calculation means for calculating misregistration values from detection results of said first detection means and said second detection means; and control means for controlling an image forming condition by said image forming means based on the misregistration values, wherein the misregistration detection patterns include a linear first reference mark and a first detection mark to be detected by said first detection means, and a linear second reference mark and a second detection mark to be detected by said second detection means, said first detection means is for detecting the first reference mark and is then for detecting the first detection mark, and said second detection means is for detecting the second detection mark and is then for detecting the second reference mark, characterized in that the linear first reference mark and the linear second reference mark are traverse line marks and make 90° as an angle with the moving direction of the transfer member and the first detection mark and second detection mark are slant marks and make an acute angle with the moving direction of the transfer member, and the first reference mark and the second detection mark are arranged so that a detection timing of the first reference mark by said first detection means and a detection timing of the second detection mark by said second detection means are concurrent timings when no misregistration occurs on the transfer member, and the second reference mark and the first detection mark are arranged so that a detection timing of the first detection mark by said first detection means and a detection timing of the second reference mark by said second detection means are concurrent timings when no misregistration occurs on the transfer member, when a misregistration occurs in the direction perpendicular to the moving direction of the transfer member, detection timings of the first detection mark and the second detection mark by said first detection means and said second detection means are different from detection timings when no misregistration occurs, and detection timings of the first reference mark and the second reference mark by said first detection means and said second detection means are the same as detection timings when no misregistration occurs. image forming means for forming misregistration detection patterns; a transfer member on which the misregistration detection patterns are transferred; first detection means and second detection means (6L, 6R) arranged to be juxtaposed in a direction perpendicular to a moving direction of said transfer member; calculation means for calculating misregistration values from detection results of said first detection means and said second detection means; and control means for controlling an image forming condition by said image forming means based on the misregistration values, wherein the misregistration detection patterns include a linear first reference mark and a first detection mark to be detected by said first detection means, and a linear second reference mark and a second detection mark to be detected by said second detection means, said first detection means is for detecting the first reference mark and is then for detecting the first detection mark, and said second detection means is for detecting the second detection mark and is then for detecting the second reference mark, characterized in that the linear first reference mark and the linear second reference mark are traverse line marks and make 90° as an angle with the moving direction of the transfer member and the first detection mark and second detection mark are slant marks and make an acute angle with the moving direction of the transfer member, and the first reference mark and the second detection mark are arranged so that a detection timing of the first reference mark by said first detection means and a detection timing of the second detection mark by said second detection means are concurrent timings when no misregistration occurs on the transfer member, and the second reference mark and the first detection mark are arranged so that a detection timing of the first detection mark by said first detection means and a detection timing of the second reference mark by said second detection means are concurrent timings when no misregistration occurs on the transfer member, when a misregistration occurs in the direction perpendicular to the moving direction of the transfer member, detection timings of the first detection mark and the second detection mark by said first detection means and said second detection means are different from detection timings when no misregistration occurs, and detection timings of the first reference mark and the second reference mark by said first detection means and said second detection means are the same as detection timings when no misregistration occurs.