An RE123-based superconducting wire (10) of the invention includes: a substrate (11); an intermediate layer (12) provided above the substrate (11); and an oxide superconducting layer (14) that is provided above the intermediate layer (12) and is made of an oxide superconductor expressed by a composition formula of RE 1 Ba 2 Cu 3 O 7-´ where RE represents one kind of or two or more kinds of rare earth elements in the formula, wherein an Hf-containing compound of 0.5 to 10 mol% is introduced into the oxide superconducting layer (14), a different phase containing Hf is dispersed in the oxide superconducting layer (14) as a flux pinning center, and the a-axial-ratio of the oxide superconducting layer (14) is less than or equal to 1.5%.