1. A substrate holding structure comprising:a cylindrical side wall portion that forms an accommodating space;
a holding wall portion protruding inward of the accommodating space from the side wall portion;
a plurality of press fit terminals held by the holding wall portion, protruding toward an opening of the side wall portion, and pressedly inserted into holes of a substrate accommodated in the accommodating space; and
a flexible arm portion protruding toward the opening from a position closer to the side wall portion than the press fit terminals of the holding wall portion, and having a hook portion configured to lock a surface on the opening side of the substrate, wherein
distal end positions of the press fit terminals and the arm portion are located closer to the holding wall portion than an end surface on the opening side of the side wall portion.