A composite sintered body according to the present invention contains at least cubic boron nitride and a binder. Cubic boron nitride has a continuous skeleton structure as a result of bonding of a plurality of first cubic boron nitride particles to each other. The binder has a continuous structure as a result of bonding of a plurality of binder particles to each other, that are present in a region except for a bonding interface where the first cubic boron nitride particles are bonded to each other. Second cubic boron nitride particles isolated from the first cubic boron nitride particles forming the skeleton structure are dispersed in the continuous structure of the binder particles.