(A) A compounding agent for diene rubbers containing a silicone resin represented by formula (1) can, when added to a rubber composition, provide a rubber composition that can achieve desired hardness, tensile properties and durability without deteriorating processability, abrasion resistance and low fuel consumption performance of the composition. Formula (1): (SiO)(RSiO)(R2 SiO)(R3 SiO)(RO) , wherein in the formula, each R independently represents a C1-8 alkyl, aralkyl or aryl group which may be substituted with a hydrogen atom or a halogen atom; at least 50 mol% of R is a methyl group; R represents a hydrogen atom, a methyl group, an ethyl group, a n-propyl group, an i-propyl group or an acetyl group; at least 20 mol% of R is a hydrogen atom; a, b, c and d are numbers satisfying 0 ≤ a < 1, 0 < b ≤ 1, 0 ≤ c < 1, 0 ≤ d < 1 and a+b+c+d = 1; and e is a number satisfying 0 ≤ e ≤ 2.
