The present disclosure relates to an electric wire connection structure including one or more copper-based conductor covered electric wires having a copper-based conductor covered part and exposed part; and one or more aluminum-based conductor covered electric wires having an aluminum-based conductor covered part and exposed part. An ultrasonic joint part is provided at a conductor stacked part in which the copper-based conductor exposed part and the aluminum-based conductor exposed part are superposed. A total contacting length L which is a summed length of a part at which the copper-based conductor exposed part and the aluminum-based conductor exposed part contact and a summed length x of a contour line of a space S formed at a part at which the copper-based conductor exposed part and the aluminum-based conductor exposed part are separate in a joint interface of the ultrasonic joint part satisfy a relational expression of (x/L)×100≤10% based on cross-section observation.