PURPOSE: To produce a diamond-based sintered body contg. a reduced number of residual pores as structural defects by using a standard HIP device.

CONSTITUTION: Many diamond particles are coated with an Ni or Co alloy by electroless plating and many particles of one or more kinds of hard materials selected among hard carbide, boride, nitride, silicide, oxide and tool steel are coated with an Ni or Co alloy by electroless plating. They are mixed, compression-molded and heated in vacuum or in gaseous hydrogen and the resulting presintered body is heated at 1,000-1,150°C under 1,000-3,000 kg/cm2 pressure by an HIP device. The mixture of many diamond particles with alloy coating films subjected to liq. phase sintering with many hard material particles with alloy coating films subjected to liq. phase sintering is subjected to liq. phase sintering.