A cubic boron nitride sintered material comprising: more than or equal to 50 volume% and less than 80 volume% of cubic boron nitride grains; and more than 20 volume% and less than or equal to 50 volume% of a binder phase, wherein the binder phase includes at least one selected from a group consisting of a compound composed of at least one element selected from a group consisting of a group 4 element, a group 5 element, a group 6 element in a periodic table, and aluminum, and at least one element selected from a group consisting of nitrogen, carbon, boron, and oxygen, and a solid solution originated from the compound, and when an oxygen content is measured in a direction perpendicular to an interface between cubic boron nitride grains using TEM-EDX using the method described in the description, a first region having an oxygen content larger than an average value of an oxygen content of a cubic boron nitride grain exists, the interface exists in the first region, and a length of the first region along the direction perpendicular to the interface is more than or equal to 0.1 nm and less than or equal to 10 nm, the average value of an oxygen content of a cubic boron nitride grain being the average of the oxygen content of the cubic boron nitride grain in a region between a line L1 and a line L2 in the cross section of the cubic boron nitride sintered material, line L1 being an imaginary line located at a distance of 20 nm from the interface between the cubic boron nitride grains toward the inner cubic boron nitride grain of the cubic boron nitride grains, line L2 being an imaginary line located at a distance of 30 nm from the interface between the cubic boron nitride grains toward the inner one of the cubic boron nitride grains. the binder phase includes at least one selected from a group consisting of a compound composed of at least one element selected from a group consisting of a group 4 element, a group 5 element, a group 6 element in a periodic table, and aluminum, and at least one element selected from a group consisting of nitrogen, carbon, boron, and oxygen, and a solid solution originated from the compound, and when an oxygen content is measured in a direction perpendicular to an interface between cubic boron nitride grains using TEM-EDX using the method described in the description, a first region having an oxygen content larger than an average value of an oxygen content of a cubic boron nitride grain exists, the interface exists in the first region, and a length of the first region along the direction perpendicular to the interface is more than or equal to 0.1 nm and less than or equal to 10 nm, the average value of an oxygen content of a cubic boron nitride grain being the average of the oxygen content of the cubic boron nitride grain in a region between a line L1 and a line L2 in the cross section of the cubic boron nitride sintered material, line L1 being an imaginary line located at a distance of 20 nm from the interface between the cubic boron nitride grains toward the inner cubic boron nitride grain of the cubic boron nitride grains, line L2 being an imaginary line located at a distance of 30 nm from the interface between the cubic boron nitride grains toward the inner one of the cubic boron nitride grains. <EOS>