PURPOSE: To obtain a scanning exposure device which is capable of projecting a picture on a large original plate onto a exposure object for exposure keeping high in throughput and exposure accuracy.

CONSTITUTION: An original plate 3 is supported nearly vertical in position, whereby a projection optical system 2 can be protected against trouble caused by the deformation of the original plate 3, and furthermore the projection optical systems 2 where an image which is equal in size and stands normal in position can be obtained are arranged, whereby a support, means 7 which supports an exposure object 4 is scanned only in a horizontal direction for light exposure even if the original plate 3 is supported vertical in position, and the support means 7 is not required to be scanned or stepped in a vertical direction, so that a scanning exposure device of this constitution is capable of being simplified in structure. A exposure process is finished through alignment and scanning carried out once, so that it is capable of being enhanced in throughput as compared with a conventional exposure method where alignment and scanning exposure are required to be carried out a few times.