1. A method of inspecting pattern defects of printed wiring boards of the same type by comparing pattern data of said printed wiring boards, said method comprising the steps of: placing a first printed wiring board having positioning marks being in prescribed positional relation to positioning marks of a wiring pattern on a table driven in a sub scanning direction; reading said marks of said first printed wiring board to find the amount of deviation of said first printed wiring board with respect to a reference position in an inspection system and thereafter performing image acquisition of an inspected area of said first printed wiring board by sequential scanning thereby to store obtained pattern data in a memory unit; placing a second printed wiring board having the same positioning marks as said marks on said table; reading said marks of said second printed wiring board thereby to find the amount of deviation of said second printed wiring board with respect to said reference position in said inspection system in order to find an amount of relative misregistration between said second printed wiring board with respect to said first printed wiring board by comparing the read marks of said first and second printed wiring boards; and controlling reading of pattern data of said first printed wiring board stored in said memory unit on the basis of said amount of said relative misregistration when said inspected area of said second printed wiring board is subjected to image acquisition while controlling arrangement of said read pattern data thereby to compare both pattern data in pixel data correspondence on the basis of pattern data of said second printed wiring board obtained by sequential scanning.