Abstract: An LSI system in which a plurality of LSIs having different scan systems are provided on an identical printed circuit board. The LSI system includes a common scan data-in terminal commonly provided for the plurality of LSIs on the printed circuit board, and a common scan data-out terminal commonly provided for the plurality of LSIs on the printed circuit board. The plurality of LSIs are classified into a plurality of groups, each group including at least one LSI having an identical scan system. Each LSI has a scan data-in pin and a scan data-out pin. Each group is connected in series or in parallel with each other, by way of the scan data-in pin and the scan data-out pin of the corresponding LSI, between the common scan data-in terminal and the common scan data-out terminal. By the above constitution, it is possible to decrease the number of external terminals to be provided on the printed circuit board for the scan operation.