A connection structure of an electronic component and terminal metal fittings includes a relay in which a plurality of terminals are projected from a relay body having a rectangular parallelepiped shape, terminal metal fittings that are fitted in the respective terminals, and a holding member in which the relay and the terminal metal fittings are accommodated. The holding member has a component body accommodating portion that accommodates the relay body, terminal accommodating portions each accommodating the distal end portion of corresponding one of the terminals and corresponding one of the terminal metal fittings, a groove portion that positions an erroneous-insertion prevention projecting portion therein when the relay is inserted in a normal orientation, and a contact portion that is brought into contact with the erroneous-insertion prevention projecting portion when the relay is inserted in an erroneous orientation.