A sintered body, containing zinc, magnesium and oxygen as constituent elements, wherein the atomic ratio of zinc to the sum of zinc and magnesium [Zn/(Zn+Mg)] is 0.20 to 0.75, the atomic ratio of magnesium to the sum of zinc and magnesium [Mg/(Zn+Mg)] is 0.25 to 0.80, and the sintered body consists of a single crystal structure as measured by X-ray diffraction.