An object is to raise both the wear resistance and chipping resistance of diamond sintered compacts while taking advantage of the characteristics of highly chipping-resistant microfine-grain diamond sintered compacts. A sintered diamond layer 3 is formed by sintering diamond grains and a binder on a cemented carbide substrate 2. This sintered diamond layer 3 comprises a main diamond layer 4 and a Co-rich diamond layer 5 that is present between the main diamond layer 4 and the cemented carbide substrate 2 and that has a Co content larger than that of the main diamond layer 4; the main diamond layer has a residual compressive stress of 1.5 GPa to 3 GPa.