A cubic boron nitride sintered body which comprises 50% by volume or more and 75% by volume or less of a cubic boron nitride, and 25% by volume or more and 50% by volume or less of a binder phase and inevitable impurities, wherein, the binder phase contains an Al compound and a Zr compound, the Al compound contains an Al element, and at least one element selected from the group consisting of N, O and B, the Zr compound contains a Zr element, and at least one element selected from the group consisting of C, N, O and B, at a polished surface of the cubic boron nitride sintered body, when a number of a plurality of line segments drawn radially at equal intervals from a center of gravity of the Zr compound to a boundary of the Zr compound and a portion of a composition other than the Zr compound is made N, provided that N is 8 or more, and among the line segments, at the boundary of the Zr compound and the portion of a composition other than the Zr compound, a number of the line segments contacting with the cubic boron nitride is made n, then a number of the Zr compound satisfying a relation of n/N being 0.25 or more and 0.8 or less is 40% or more based on a total number of the Zr compound, wherein the Zr compound is 1% by volume or more and 4% by volume or less based on the whole cubic boron nitride sintered body, wherein the Zr compound contains ZrB 2 and ZrO 2, a crystal structure of the ZrO 2 is formed in a state of tetragonal, or both of tetragonal and cubic being intermixed, when a peak intensity at a plane of the ZrB 2 is made I 1, a peak intensity at a plane of the tetragonal ZrO 2 is made I 2t, and a peak intensity at a plane of the cubic ZrO 2 is made I 2c in X-ray diffraction, a ratio [I 1 /(I 2t +I 2c)] of an intensity of I 1 based on a sum of intensities of I 2t and I 2c is 0.5 or more and 5 or less, and wherein an average grain size of the cubic boron nitride is 0.2 μm or more and 0.8 μm or less. 50% by volume or more and 75% by volume or less of a cubic boron nitride, and 25% by volume or more and 50% by volume or less of a binder phase and inevitable impurities, wherein, the binder phase contains an Al compound and a Zr compound, the Al compound contains an Al element, and at least one element selected from the group consisting of N, O and B, the Zr compound contains a Zr element, and at least one element selected from the group consisting of C, N, O and B, at a polished surface of the cubic boron nitride sintered body, when a number of a plurality of line segments drawn radially at equal intervals from a center of gravity of the Zr compound to a boundary of the Zr compound and a portion of a composition other than the Zr compound is made N, provided that N is 8 or more, and among the line segments, at the boundary of the Zr compound and the portion of a composition other than the Zr compound, a number of the line segments contacting with the cubic boron nitride is made n, then a number of the Zr compound satisfying a relation of n/N being 0.25 or more and 0.8 or less is 40% or more based on a total number of the Zr compound, wherein the Zr compound is 1% by volume or more and 4% by volume or less based on the whole cubic boron nitride sintered body, wherein the Zr compound contains ZrB 2 and ZrO 2, a crystal structure of the ZrO 2 is formed in a state of tetragonal, or both of tetragonal and cubic being intermixed, when a peak intensity at a plane of the ZrB 2 is made I 1, a peak intensity at a plane of the tetragonal ZrO 2 is made I 2t, and a peak intensity at a plane of the cubic ZrO 2 is made I 2c in X-ray diffraction, a ratio [I 1 /(I 2t +I 2c)] of an intensity of I 1 based on a sum of intensities of I 2t and I 2c is 0.5 or more and 5 or less, and wherein an average grain size of the cubic boron nitride is 0.2 μm or more and 0.8 μm or less.