A color image forming apparatus including an image bearing member movable along an endless path, on which color toner images are formed, a transfer material supporting member movable along an endless path for supporting a transfer material and conveying it to an image transfer position where the color toner images are superimposed and transferred sequentially to the transfer material. Also provided are a first driving motor for driving the image bearing member, and a second driving motor, separately provided from the first motor, for driving the transfer material supporting member. In addition, the apparatus includes a detector for detecting the speed of the surface of the transfer material, a discriminator for determining whether the speed variations detected by the detector are within a tolerable range, and a control, responsive to the discriminator, for stopping the operation of a subsequent image transfer step when the detected speed variation is beyond the tolerable range, and for repeating latent image forming, developing, and transfer steps.