PURPOSE:To prevent cracks at the bottoms of grooves in particular by specifying the hardness of a shore A of a inner rubber installed on a tread and a foaming coefficient of a foaming rubber forming an outer rubber layer respectively and covering the outer surface of the outer rubber layer by means of a specified sheathing layer. CONSTITUTION:A tire 1 has its tread 3 provided with an outer and an inner rubber layers 3A, 3B. Also, the tread 3 has a region 3a on both sides thereof and a region 3b on the center thereof provided respectively with a groove 10 in a lateral direction and grooves 11A, 11B in a peripheral direction, by which a land portion 12 is formed. In such a constitution, the outer rubber layer 3A is formed by a foaming rubber which has a foaming coefficient of 5% to 50%, and has the ratio shared by the tread 3 in volume set to be at least 10%. Also, the inner rubber layer 3B has the hardness of a shore A set to be 54 deg. to 80 deg. to get higher than the outer rubber layer 3A. Then, the outer rubber layer 3A has its outer surface covered by a sheathing layer 9, not exceeding 1mm in thickness, comprising a smaller foaming coefficient of a rubber seat than that of the foaming rubber.