Points obtained by plotting flexural rigidity EI measured at ten sites on a shaft are defined as from T (1) to T (10) in this order from the head side, and the formula representing a line K that passes the T (1) and the T (10) is defined as [Y=aX+b1]. The values at the Y-intercepts on the lines that are parallel to the line K and that pass the points of from T (2) to T (9), respectively, are defined as from b2 to b9, respectively, and the minimum value among the values at the Y-intercepts b2 to b9 is defined as bmin. Slope "a" of the line K is 0.04 or greater and 0.06 or less; every one of the b3, b4, b5, b6, b7 and b8 is smaller than b1; and the bmin is any one of b4 to b7. The value (b1-bmin) is 30 (Nm.sup.2) or greater and 40 (Nm.sup.2) or less, and the value (b9-b1) is 4 (Nm.sup.2) or greater and 15 (Nm.sup.2) or less. This shaft either has a high-strength straight layer and a hoop layer, or has a textile layer.