PURPOSE: To easily detect the bridge by flickering only bridge part of the test printed circuit board on the composed image with the image of the test printed circuit board and the image of the standard printed circuit board.

CONSTITUTION: Image of the standard printed board 1 and the image of the test printed board 1 are projected on the same picture to obtain composed image 3. Under this condition, if image on the test printed board 1 is flickered by a flickering device 5, only bridge 2 of the composed image flickers., i.e., if image on the test printed board 1 is flickered, soldered part is always illuminated on the composed image 3 and only bridge 2 is repeatedly flickered.