PURPOSE: To provide a method for preparing a Bi-Sr-Ca-Cu-O-based superconducting thin film having high Tc by easy control without requiring annealing.

CONSTITUTION: In preparing a superconducting thin film by using Bi oxide powder (or Bi metal), Bi compound oxide (Bi2Sr2Cu1Ox) powder and a sintered material of Ca1Cu1Ox, etc., as Bi supply source and by sputtering the substances as a target, an oxide reduced into a state of an average valence of constituent Bi of ≥ divalent value and <trivalent value (oxide has the surface modified into a low-valent state by sputtering on given oxide powder in an atmosphere containing Ar and oxygen; oxide having Bi bond energy shifted to a low-bond energy side) is used as the Bi oxide powder. Single crystal of MgO(100) is used as a substrate, the temperature of the substrate is 760°C, 1Pa of Ar+O2 (volume ratio of 4:1) is used as a sputtering gas and a Bi-Sr-Cu-O layer and a Ca-Cu-O layer are alternately laminated.