PURPOSE: To detect all bridges having the optional widths including the one equivalent to the circuit width by extracting the branching point between a check pattern and a pattern to be checked and comparing both patterns with each other.

CONSTITUTION: A branching point is extracted out of a binary picture 1 of a normal pattern to be checked and the branching point information 31 is obtained. The information 31 is once stored in a storage circuit 5 for data to be checked via a switch circuit 4. Then a branching point extracting circuit 2 extracts the branching points out of a binary picture 1 of a check pattern between a land and a circuit and between the circuit and a bridge pattern 9 respectively. Thus the branching point information 31' - 33' are obtained and stored successively into a check data storage circuit 6. The branch point information are simultaneously read out of both circuits 5 and 6, and a comparator 7 checks the presence or absence of both branching point information. Then the branching points 32' and 33' are detected via a bridge having the width equivalent to the circuit width and outputted as a bridge detecting signal 8. Then the branching point information 3 on a printed circuit board to be checked is stored in the circuit 6 via the circuit 4 to undergo the comparison and the check.