Abstract: A method of checking defectively fused ampoules wherein a head portion of a fused ampoule is projected on a light receiving screen so as to focus an image of the heat portion thereon, a focused image is scanned with a plurality of scanning lines running in the diametral direction of the focused image and sequentially sweeping in the longitudinal direction thereof to produce a plurality of edge signals corresponding to the scanning lines, the number of edge segments and the inner and outer widths are measured from each of the edge signals, measured values are compared with predetermined logical references set for the number of edge segments and inner and outer widths, and the fused ampoule is judged defective when the measured values are incongruous to the logical references.