PURPOSE: To enable the detection of inferior operation without missing the same, by providing function for performing a test by strobing the output of testing FF in predetermined timing.

CONSTITUTION: The control part 11a of a tester 1a performs strobing due to CLKIV as timing previous from a second clock signal CLKII and, on the basis of the output thereof, one cycle delayed expected value data DATA2n-1 is sent out other than expected value data DATA1n, DATA2n to perform the testing of DEF2. In addition, the control part 11a controls a delay circuit DL14c and a selector circuit MPX15c to send out CLKIV to a comparator citcuit 13b and collates the Q-output of FF2 with separate DATA2n-1 on the basis of CLKIV and, when no coincidence is obtained, abnormal operation is judged.