An optical fiber holding structure includes: a structure main body having a prismatic shape; a through hole into which an optical fiber is inserted; a protruding portion having a columnar shape projecting from the structure main body and configured to be inserted into an opening portion of a substrate; and a contact portion configured to abut on a surface of the substrate to position an optical element and the optical fiber at a predetermined distance. The through hole is formed so as to penetrate from a surface of the structure main body through which the optical fiber is inserted to an end surface of the protruding portion, and at least one side surface of the structure main body is flush with at least one side surface of the protruding portion.