An inspecting method for grasping the inspection result on an intermediate (or an n-th) treatment without long extension of time, in case predetermined treatments of a predetermined number (N times) are exerted on a plurality of sheets running on a conveyor line, before all the treatments of N-times are ended. The inspecting method for inspecting an object subjected to the predetermined treatment includes performing the predetermined treatment repeatedly by the N-times (N: a natural number of 2 or more) sequentially on the individual objects being conveyed on the conveyor line, and an inspecting step of testing such a leading one of the objects as has been subjected to the n-th (n: a natural number of 1 or more but N or less) treatment, and returning the tested object to after such one of the targets as was subjected to the n-th treatment.