PURPOSE: To achieve an accurate control of serial numbers by arranging a device equipped with a photoelectric sensor receiver or the like having a means for reading serial numbers, a method to judge specified positional information among parts for mounting electronic component-packaged substrates or the like.

CONSTITUTION: First, information is stored into an information processor 9 for managing serial numbers on layout positions of individual parts 4 for mounting electronic component-packaged substrates of a group 3 thereof beforehand. Then, after or when a worker mounts an electronic component-packaged substrate 1 for an operation test at the mounting section 4, a bar code 2 on the substrate 1 is read by a serial number reading means freely at any time. At this point, light emitted from a projector photoelectric sensor 7 mounted on a bar code reader 6 is detected with a receiver photoelectric sensor 5 mounted on the mounting part 4 and the resulting switching information is stored into a register device 8 by a position detecting means reading serial numbers as layout position information. An information processor performs a corresponding operation of the information by a serial number position information corresponding means to accomplish a management of the serial numbers.