When a cross-sectional area of each zirconia crystal grain is calculated in an image of a cross section of a zirconia sintered body； a converted crystal grain size of each zirconia crystal grain is calculated based on the cross-sectional area on the assumption that each zirconia crystal grain has a circular cross-sectional shape； the zirconia crystal grains are classified into a class of smaller than 0.4µm, a class of from 0.4µm to smaller than 0.76µm, and a class of 0.76µm or greater based on the converted crystal grain size； a total cross-sectional area of the zirconia crystal grains is calculated in each of the classes； and a rate of the cross-sectional area to a total cross-sectional area of all zirconia crystal grains whose cross-sectional area has been calculated is calculated in each class, the rate of the cross-sectional area of the zirconia crystal grains in the class of the converted crystal grain size of smaller than 0.4µm ranges from 4% to 35%, the rate of the cross-sectional area of the zirconia crystal grains in the class of the converted crystal grain size of from 0.4µm to smaller than 0.76µm ranges from 24% to 57%, and the rate of the cross-sectional area of the zirconia crystal grains in the class of the converted crystal grain size of 0.76µm or greater ranges from 16% to 62%.
