An inner casing according to the present invention includes a hole which is a holding portion that is provided at the center of a base portion having a planar shape so as to protrude in a direction orthogonal to a principal surface of the base portion and hold a capsule endoscope and a plurality of step portions each protruding from a side surface of the hole and abutting on an area of an outer surface of a hemispheric dome portion, which is located inside an optical viewing angle of the capsule endoscope and which does not contribute to generation of an image captured by the capsule endoscope to realize alignment in a longitudinal direction of the capsule endoscope.
