Abstract: The composite sintered body of the invention is a composite sintered body, containing 20 volume % or more and 80 volume % or less of cubic boron nitride particles, and a binder; wherein the binder contains at least one selected from the group consisting of nitrides, carbides, borides, and oxides of elements in the group 4a, elements in the group 5a, and elements in the group 6a in the periodic table, and solid solutions thereof, at least one selected from the group consisting of simple substances of Zr, Si, Hf, Ge, W and Co, compounds thereof, and solid solutions thereof, and a compound of Al; and when the composite sintered body contains therein W and/or Co, the total weight of the W and/or Co is less than 2.0 weight % and further the composite sintered body contains therein one or more of the Zr, Si, Hf and Ge (hereinafter referred to as “X”), and when the composite sintered body contains the X, the amount of each of the X is 0.005 weight % or more and less than 2.0 weight %, X/(X+W+Co) is 0.