A system for determining the existence of a selected size and orientation of copy papers to be used in a copying machine is provided. Such a system is particularly useful when applied to a copying machine for making copies from an original with various magnification ratios. The system has a size indicator as well as an orientation indicator so that when installed copy papers do not satisfy the condition required by a desired mode of copying operation, it will be clearly indicated whether the size and/or the orientation of the installed copy papers are inappropriate. Thus, convenience in using a copying machine has been greatly improved.