A rubber composition comprising a vulcanizable rubber, a reinforcing filler, a
softening agent, and other reagents for rubber to which is added in a specific
amount of a sulfur compound having the formula (I):
wherein R1 represents an organic group, x is a number of 3 to
5 on average, and n is an integer of 1 to 100, or a specific sulfur compound (1)
and sulfur (2), and optionally a thiazole base, sulfenamide base, thiuram base,
and/or diothio acid base vulcanization accelerator (3).
