An imaging device support structure includes a master flange having an opening portion through which an optical axis A passes, an imaging device which is attached to the master flange via the attachment plate and is positioned in the opening portion as viewed in an optical axis A direction, and a shielding member which shields a gap between the master flange and the imaging device in the opening portion. The shielding member is pressed against the opening edge of the first opening portion. The opening edge of the first opening portion has a substantially polygonal shape with corner portions which outwardly protrude.