Disclosed is an aluminum-diamond composite having both high thermal conductivity and thermal expansion coefficient close to those of semiconductor elements, which is improved in platability in the surface and surface roughness so that the composite becomes suitable for use as a heatsink of a semiconductor element or the like. Specifically disclosed is a plate-like aluminum-diamond composite containing diamond particles and a metal mainly composed of aluminum. The aluminum-diamond composite is composed of a composite part and surface layers formed on both sides of the composite part, and the surface layers are composed of a material containing a metal mainly composed of aluminum. The diamond particle content is 40-70% by volume of the entire aluminum-diamond composite.