Provided is a sintered oxide compact that has high electric conductivity and a small B-value (temperature coefficient), and is suitable for use as an electrically conductive material, and a circuit board that uses the sintered oxide compact. The sintered oxide compact is represented by a composition formula: REaCobNicOx (where RE represents a rare earth element, a + b + c = 1, and 1.3 ‰¤ x ‰¤ 1.7), the sintered oxide compact includes a perovskite phase with a perovskite-type oxide crystal structure, and the a, b, and c satisfy the following relationships: 0.459 ‰¤ a ‰¤ 0.535, 0.200 ‰¤ b ‰¤ 0.475, and 0.025 ‰¤ c ‰¤ 0.300.