To improve the inspection accuracy when insulation between a plurality of conductor patterns is inspected.

When the insulation between 16 conductor patterns is inspected, first to third and sixth to tenth conductor patterns, third to sixth and ninth to twelfth conductor patterns, first to fourth, tenth, eleventh, fifteenth, and sixteenth conductor patterns, and second to seventh, fourteenth, and fifteenth conductor patterns are set as a first group, and are connected to a low potential. First connection processing in A-D states in which the other conductor patterns are connected to a high potential, and second connection processing in E-H states are executed in a previously determined sequence. In the second connection processing, in the same combination as that of the conductor patterns set as each group in the first connection processing in each of the A-D states, the conductor patterns are connected to respective potentials inverse to the potentials in each first connection processing.