Image pickup element mounting substrate and image pickup device

An image pickup element mounting substrate, comprising:

• a frame body composed of an insulating layer, a through hole being defined by an internal periphery of the frame body, the frame body being provided with a frame-body recess which opens on a lower outer surface of the frame body;
• an electronic component mounted in the frame-body recess;
• and
• a flat plate which is disposed on the lower outer surface of the frame body and covers an opening of the through hole while being partly kept in out-of-contact with the electronic component, the flat plate comprising an image pickup element mounting section at a first part of an upper surface of the flat plate, the first part of the upper surface being surrounded by the frame body,
• a lower surface of the electronic component being located above a level of a lower surface of the flat plate.