1. A method of inspecting the accuracy at which desired regions are stitched on a material on which regions are exposed successively to form a pattern, said method comprising the steps of: selecting an inspected region containing at least two specified pattern elements existing in said exposed regions; detecting signals arising from said inspected region; detecting positions of said specified pattern elements within said inspected region from said detected signals; obtaining data about a reference region corresponding to said inspected region and treating said data as reference data; finding positions of said specified pattern elements within said reference region from said reference data; and comparing said positions of said specified pattern elements within said reference region with said positions of said specified pattern elements within said inspected region, whereby inspecting accuracy at which the exposed regions within said inspected region are stitched.