It is possible to reduce pulling-out resistance of a knife blade from a tire while highly securing fall-preventing effect on block. A tread portion 2 has a block 7 provided with sipeings 10. The sipeing 10 has a zigzag portion 11 in an opening edge shape J at a block surface S, and zigzag displacement portions which are displaced toward one end of a longitudinal direction Fn and the other end are alternately repeated to form the zigzag portion 11 in a depth direction. When displacement amounts of a zigzag displacement portion 15U on the side of block surface, a zigzag displacement portion 15L on the side of sipeing bottom and an intermediate zigzag displacement portion 15M in a direction Fv perpendicular to the longitudinal direction Fn are defined as W1, W3 and W2, the following expressions are satisfied. W1≧W2 0.7×W2≧W3>0