A plurality of photomasks used to manufacture the same semiconductor device, each of the photomasks having a plurality of mutually replaceable unit regions set therein, are inspected to detect a defect. It is determined whether or not the detected defect has a redundancy defect positioned in a unit region replaceable with another unit region to remedy the photomask. Then, when inspecting the second or subsequent photomask, a unit region including the coordinate of a redundancy defect detected in another photomask inspected previously is set to be a non-inspection region, and the non-inspection region is not inspected.