PURPOSE: To obtain a device capable of rapidly inspecting a defective via hole formed to a multilayer board accurately in a nondestructive manner by providing each specific light source, polarizing means, photo-detecting means and display means.

CONSTITUTION: A light source 2 emitting original inspection light OL and a polarizing means 3 converting original inspection light OL into inspection light L as linearly polarized light are provided in a via-hole inspection device inspecting defective via holes formed to a multilayer board with an insulating layer and a wiring layer. A photo-detecting means 8, which forms crossed Nicols together with the polarizing means 3 and through which only reflected light having the specific plane of polarization in reflected light transmitted through the insulating layer having a specified thickness range in the vicinity of a normally formed via hole and reflected by the wiring layer in inspection light L applied to a substance to be inspected 6 is transmitted, is provided. Display means 9, 10 for visualizing reflected light transmitted through the photo-detecting means 8 are provided. The display means represent an image sensing device 9 and a display 10.