1. An inspection apparatus comprising: a wafer stage for carrying a wafer; an illumination module which irradiates an inspection beam on the wafer carried on said wafer stage; a detection module which detects scattering rays or reflection rays from the wafer on said wafer stage and outputs an image signal; a coordinates control module which stores information about the arrangement of individual inspection areas on said wafer; an imperfect area recognition module which recognizes, based on the inspection area arrangement information stored in said coordinates control module, an imperfect inspection area interfering with a wafer edge; and a validity degree decision module which decides, from a difference between an image signal of the whole of an inspection area and an image signal of the whole of a reference area, a degree of validity of the inspection area.