An oxide superconductor of an embodiment includes an oxide superconductor layer having a continuous Perovskite structure including rare earth elements, barium (Ba), and copper (Cu). The rare earth elements include a first element which is praseodymium, at least one second element selected from the group consisting of neodymium, samarium, europium, and gadolinium, at least one third element selected from the group consisting of yttrium, terbium, dysprosium, and holmium, and at least one fourth element selected from the group consisting of erbium, thulium, ytterbium, and lutetium. When the number of atoms of the first element is N(PA), the number of atoms of the second element is N(SA), and the number of atoms of the fourth element is N(CA), 1.5×(N(PA)+N(SA))≤N(CA) or 2×(N(CA)−N(PA))≤N(SA) is satisfied.