An object of the invention is to provide a method and apparatus for observing inside structures and a specimen holder, wherein aging degradation of a good sample to a bad sample can be tracked in the same field of view, using the same specimen in order to determine the mechanism of failure. The present invention is a method for observing inside structures. The method comprises irradiating a specimen with a corpuscular beam generated from a corpuscular beam source, detecting transmitted particles transmitted by the specimen, applying a voltage to a portion of the specimen, and observing of a detection status of the transmitted particles in the voltage-applied portion as needed.