According to one embodiment, an oxide superconductor includes an oriented superconductor layer and an oxide layer. The oriented superconductor layer contains fluorine at 2.0×1016-5.0×1019 atoms/cc and carbon at 1.0×1018-5.0×1020 atoms/cc. The superconductor layer contains in 90% or more a portion oriented along c-axis with an in-plane orientation degree (Δφ) of 10 degrees or less, and contains a LnBa2Cu3O7-x superconductor material (Ln being yttrium or a lanthanoid except cerium, praseodymium, promethium, and lutetium). The oxide layer is provided in contact with a lower surface of the superconductor layer and oriented with an in-plane orientation degree (Δφ) of 10 degrees or less with respect to one crystal axis of the superconductor layer. Area of a portion of the lower surface of the superconductor layer in contact with the oxide layer is 0.3 or less of area of a region directly below the superconductor layer.