A sheet-shaped aluminum-diamond composite containing a prescribed amount of a diamond powder wherein a first and second peak in a volumetric distribution of particle sizes occurs at 5-25 μm and 55-195 μm, and a ratio between an area of a volumetric distribution of particle sizes of 1-35 μm and 45-205 μm is from 1:9 to 4:6, the composite including an aluminum-containing metal as the balance, wherein the composite is covered, on both main surfaces, with a surface layer having prescribed film thicknesses and containing 80 vol % or more of an aluminum-containing metal, two or more Ni-containing layers are formed on at least the surface layer, the Ni-containing layers being such that a first and second layer from the surface layer side are amorphous Ni alloy layers having prescribed thicknesses, and an Au layer having a prescribed thickness is formed as an outermost layer.