The present invention relates to a defect inspection apparatus for a phase shift mask that is capable of detecting phase shifter defects that cannot be detected by conventional inspection techniques, by a simple method using an optical method and a comparison of electric signals. The insulating substrate has substantially the same shape as that of the multilayer ceramic capacitor, viewed from a direction perpendicular or substantially perpendicular to the main surface, and has the multilayer ceramic capacitor mounted thereon so that the length direction of the multilayer ceramic capacitor substantially coincides with the length direction of the insulating substrate. The apparatus may also include a vacuum-tight optical window for observing the sample and a shutter for protecting the optical window from debris while the sample is prepared in the ion beam. In some implementations, the NDR device is arranged to mitigate leakage in a storage device using a two-terminal connection.