A connection structure of high-temperature superconducting wires includes first and second superconducting wires which are high-temperature superconducting wires respectively having a base material consisting of metal or alloy, and an oxide superconducting layer formed on the base material. A joint portion containing a superconducting connection portion between the first and second superconducting wires joins the first and second superconducting wires in a positional relationship facing the surfaces of first and second superconducting layers which are the oxide superconducting layers of each of the first and second superconducting wires, are opposed to each other. In a base material of at least one superconducting wire among the first and second superconducting wires, a first portion constituting the joint portion is thicker than a second portion not constitute the joint portion in the same base material.