An object of the present invention is to provide: a superconducting wire with a boron-containing superconductor charged or included therein, the superconducting wire further being able to have a practical critical current density; a method for manufacturing the superconducting wire, and; a superconducting magnet using the superconducting wire. The present invention is characterized in that: in a superconducting wire which has a boron-containing superconductor charged or included therein, a metal-sheathing material made of either a single metal selected from a group consisting of gold, silver, aluminum, copper, iron, platinum, palladium, nickel, stainless steel, chromium, magnesium, tantalum, niobium, titanium, tin, beryllium, tungsten, and cobalt, or an alloy consisting of a plurality of metals selected from this group, is disposed on the outer surface of the foregoing superconducting wire, the density of the superconducting wire after it has been finally processed is 80% or more of its theoretical density, and the critical temperature of the superconducting wire is 30K or more.