1. A process control method for a copying apparatus having a plurality of rotatable photosensitive members and an image transfer belt rotatable in synchronism with said photosensitive members for transferring visible images formed on said photosensitive members onto a transfer paper carried by said transfer belt, comprising the steps of; confirming a detection of a first mark provided on said transfer belt by a first sensor provided in the vicinity of said transfer belt, initiating rotations of said photosensitve members upon said confirmation such that each of said photosensitve members completes at least on revolution prior to a detection of a second mark provided on said transfer belt by a second sensor provided in the vicinity of said transfer belt after said first mark is detected by said first sensor, performing a preprocess for said photosensitive members during at least one revolution of each of said photosensitive members, initiating a copying process upon said detection of said second mark by said second sensor, and terminating movements of said photosensitive members and said transfer belt upon a subsequent detection of said first mark by said first sensor to said detection of said second mark by said second sensor.