PURPOSE: To gather even the state of a flip-flops which is not put in a scan path by inputting the output of the flip-flops which is not connected to the scan path means to a flip-flop connected to the corresponding scan path means by a flip-flop trace means when a clock is inputted.

CONSTITUTION: This system is provided with the flip-flop trace unit 13 and scan path 14 in addition to the stop flip-flop 11 and nonstop flip-flop 12. The flip-flop trace unit 13 optionally controls the clock which places the flip-flop in operation similarly to the stop flip-flop 11 to read and write data through the scan path 14. The input terminal of the flip-flop trace unit 13 is connected to a scan-in path 22 and the output terminal is connected to the input terminal of the stop flip-flop 11 through the scan path 14.