An imaging device comprising: a substrate for mounting an imaging element, comprising a base; the base comprising: a through-hole having an opening in a top surface of the base; a cover mounting region provided on the top surface, in a rim of the opening of the through-hole; a lens-housing mounting region provided on the top surface, on an outer side of the cover mounting region; an intermediate region provided on the top surface, between the cover mounting region and the lens-housing mounting region; a connecting section that enables the intermediate region to communicate with an inside wall of the through-hole; and an imaging element mounting section provided on a bottom surface of the base, and wherein the base comprises a groove that forms the connecting section; and the base is formed of a plurality of layers; and the groove is formed of a slit provided in an uppermost layer, an imaging element mounted on the imaging element mounting section of the substrate for mounting an imaging element; and when viewed in a see-through plan view, a transparent cover disposed on the cover mounting region so as to cover the opening. a substrate for mounting an imaging element, comprising a base; the base comprising: a through-hole having an opening in a top surface of the base; a cover mounting region provided on the top surface, in a rim of the opening of the through-hole; a lens-housing mounting region provided on the top surface, on an outer side of the cover mounting region; an intermediate region provided on the top surface, between the cover mounting region and the lens-housing mounting region; a connecting section that enables the intermediate region to communicate with an inside wall of the through-hole; and an imaging element mounting section provided on a bottom surface of the base, and wherein the base comprises a groove that forms the connecting section; and the base is formed of a plurality of layers; and the groove is formed of a slit provided in an uppermost layer, an imaging element mounted on the imaging element mounting section of the substrate for mounting an imaging element; and when viewed in a see-through plan view, a transparent cover disposed on the cover mounting region so as to cover the opening. a through-hole having an opening in a top surface of the base; a cover mounting region provided on the top surface, in a rim of the opening of the through-hole; a lens-housing mounting region provided on the top surface, on an outer side of the cover mounting region; an intermediate region provided on the top surface, between the cover mounting region and the lens-housing mounting region; a connecting section that enables the intermediate region to communicate with an inside wall of the through-hole; and an imaging element mounting section provided on a bottom surface of the base, and wherein the base comprises a groove that forms the connecting section; and the base is formed of a plurality of layers; and the groove is formed of a slit provided in an uppermost layer, an imaging element mounted on the imaging element mounting section of the substrate for mounting an imaging element; and when viewed in a see-through plan view, a transparent cover disposed on the cover mounting region so as to cover the opening.