This invention is directed to a paper jam detecting device for use in an electrophotographic copying machine which comprises a plurality of paper detector located along the passage of the copy paper transported during copying process, first timer adapted to count the first period of time so as to detect the leading edge of the copy paper by any one of the paper detector and second timer adapted to count the second period of time so as to detect the trailing edge of the copy paper by said one of the paper detector, whereby paper jam can be detected in case where no paper is detected on the first period of time or in case where a paper is detected on the second period of time.