A tread portion (4) of a tire includes a first vertical groove (10), a second vertical groove (12), a subvertical groove (14), a first lateral groove (16), a second lateral groove (18) and a third lateral groove (20) on a surface thereof. The tread portion (4) further includes a first block (24), a second block (26), a third block (28) and a fourth block (30). Each of the blocks (24), (26), (28) and (30) has a siping (S). The siping (S) takes a zigzag shape. Each of the blocks (24), (26), (28) and (30) has a large number of small grooves (G). The shape of the small groove (G) constitutes a part of a wavy curve extended in an axial direction. The small groove (G) has a width which is equal to or greater than 0.1 mm and is equal to or smaller than 2.0 mm and a depth which is equal to or greater than 0.1 mm and is equal to or smaller than 1.0 mm. The small groove (G) has a pitch which is equal to or greater than 0.5 mm and is equal to or smaller than 5.0 mm. The number of cycles of the wavy curve is equal to or larger than 1.0 and is equal to or smaller than 7.0.