A terminal assembly structure according to one or more embodiments includes: a terminal having a crimp portion configured to crimp and connect to a core wire of an electric wire and a fastening portion configured to be fastened by a fastening member; and a holder having a base configured to mount the terminal when fastening the terminal to the holder. The holder has a plurality of ribs extending in a fastening direction of the fastening member and arranged around the fastening portion of the terminal when the fastening portion is set and positioned onto the base.