A connection structure includes: a first wire； a second wire having a diameter smaller than a diameter of the first wire； a connection member configured to connect the first wire and the second wire, wherein a distal end portion of the first wire is inserted from an opening portion at one end of the connection member to be crimped, and a proximal end portion of the second wire is inserted from an opening portion at another end of the connection member to be crimped, the opening portion at the other end having a diameter smaller than a diameter of the opening portion at the one end.
