An embodiment of the present invention relates to a composition or filler mixture. This composition includes a thermally conductive filler (A) having a cumulative volume 50% particle diameter (D50(A)) of 0.05 μm or more and less than 1.0 μm and a cumulative volume 90% particle diameter (D90(A)) of 2.0 μm or less in a particle size distribution curve determined by laser diffractometry; a thermally conductive filler (B); and a binder component (C). The composition satisfies requirement (1) in the entire thermally conductive filler (B) used in the composition, a cumulative pore amount of pores with a pore diameter of 0.5 μm or less as calculated from a pore diameter distribution measured with a mercury porosimeter is 0.05 ml/g or less; requirement (2) the entire thermally conductive filler (B) used in the composition has a cumulative volume 50% particle diameter (D50(B)) of from 1.0 to 100 μm; and requirement (3) the entire thermally conductive filler (B) used in the composition has a cumulative volume 10% particle diameter (D10(B)) of 0.6 μm or more.