Niobium oxide sintered compact, sputtering target formed from said sintered compact, and method of producing niobium oxide sintered compact

A niobium oxide sintered sputtering target having a composition of NbOx (2<x<2.5) and a relative density of 90% or higher, wherein a ratio of an X-ray diffraction peak intensity from (110) plane of Nb to an X-ray diffraction peak intensity which is highest among intensities of X-ray diffraction peaks from (400) plane of NbO2, (001) plane of Nb2O5, and (110) plane of Nb2O5 and of X-ray diffraction peaks observable within a range of 2θ from 20° to 60° is 1% or less, and wherein a ratio of an X-ray diffraction peak intensity from a Nb12O29 (400) plane relative to an X-ray diffraction peak intensity from a NbO2 (400) plane is 10% or higher.