Provided is a rubber composition for a tire soft stiffener improved in a crack resistance and a low heat generation, wherein carbon black (A) contained in the rubber shows specific particle size distribution behavior in an aggregate mass distribution curve, and the composition contains at least one compound selected from carbon black coupling agents consisting of bismaleimide (B), alkylidene hydrazide (C), disulfane (D) and carboxylic hydrazide (E), and a heavy-duty tire produced by using the above rubber composition is further provide.