A composite sintered material suitably used as a material for a drill has a sandwich structure comprising a hard layer of a sintered diamond compact including an iron group metal sandwiched between a pair of substrates and intermediate layers. The pair of intermediate layers each has a thickness of 10 to 500 microns. The intermediate layers are bonded respectively to one of the opposite surfaces of the hard layer, with each of the intermediate layers comprising a material which has a thermal expansion coefficient of 3.0.times.10.sup.-6 to 6.0.times.10.sup.-6 /.degree.C. and which prevent the transfer of the iron group metal therethrough in the course of sintering of the hard material. The pair of substrates are bonded respectively to one of the surfaces of the intermediate layers to form a sandwich construction with the hard layer. The substrates comprise a metal or alloy having a thermal expansion coefficient lower than 6.0.times.10.sup.-6 /.degree.C. In using the composite sintered material as a blade tip for a cutting tool, the sintered diamond compact contains preferably 5 to 15 vol. % of an iron group metal, the balance being of diamond particles, and each of the substrates is composed of a sintered alloy mainly composed of WC and/or MOC having a thermal expansion coefficient lower than 4.6.times.10.sup.-6 /.degree.C.