Imaging element mounting substrate and imaging device

An imaging element mounting substrate, comprising:

• an insulating base comprising a plurality of insulating layers, the insulating base surface comprising an opening which is located at a center of the insulating base;
• a connection electrode disposed at a lower surface of the insulating base around the opening, the connection electrode connectable to an imaging element;
• and
• a plurality of light-transmission control layers which are between the plurality of insulating layers, respectively, the plurality of light-transmission control layers surrounding the opening, being disposed overlapping one another in large part as seen in a transparent plan view, and comprising inner edges located on an outside of the opening,
• an inner edge of one of the plurality of light-transmission control layers lying closer to the opening than an inner edge of another one of the plurality of light-transmission control layers as seen in a transparent plan view,
• the insulating base having, in an inner periphery of the opening of an insulating layer constituting a lower surface of the insulating base, an inclined portion which is inclined such that the opening becomes smaller in size from the lower surface as approaching an upper surface of the insulating base.