To eliminate defects in which, since an elastic yarn at an ankle part always fastens the ankle part by rubber elasticity and this state is held, and the ankle part has approximately the same thickness from a lower part to an upper part, cocks do not slip down from the ankle parts, but socks cause distortions at the upper parts of the ankle parts and the lower parts, especially parts in vicinity of ankle bones by washing of a number of times even in ankle parts incorporated with rubber and the socks slip down.

This cock is provided with month knitting part 12, an ankle knitting part 14 and a foot knitting part 16. At least the ankle knitting part 14 is furnished with one elastic member 24 knitted into a base yarn 26. The ankle knitting part 14 has a part in which no elastic member 24 is knitted in the circumference direction. The elastic member 24 knitted in the ankle knitting part has dense intervals in the vicinity of the upper end and the lower end of the elastic member. The sock is produced by knitting one elastic member into a base yarn by reciprocating a knitting machine by tacking in or laying in.