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.