The cubic boron nitride sintered body is a cubic boron nitride sintered body comprising 50% by volume or more and 75% by volume or less of a cubic boron nitride (1) and 25% by volume or more and 50% by volume or less of a binder phase and inevitable impurities, the binder phase contains an Al compound (3) and a Zr compound (2), the Al compound (3) contains Al and at least one element selected from the group consisting of N, O and B, the Zr compound (2) contains Zr and at least one element selected from the group consisting of C, N, O and B, and at the polished surface of the cubic boron nitride sintered body, when a number of a plurality of line segments (5) drawn radially at equal intervals from a center of gravity (4) of the Zr compound (2) to a portion other than the Zr compound (2) is made N, and among the line segments (5), at the boundary of the Zr compound and the portion of a composition other than the Zr compound, a number of the line segments (5) at which the Zr compound and the cubic boron nitride are contacting with each other is made n, a number of the Zr compound (2) 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 (2).