PURPOSE: To obtain steel cord having increased gap forming performance along yarn stocks and cord shape retention, improved penetration into rubber, reliability, uniformity of tire, excellent product accuracy and reliability as well as production efficiency.

CONSTITUTION: In steel cord formed by twisting yarn stocks 1 to 3, the yarn stocks 1 and 2 are twisted in the same twisting pitch P in a mutually linear contact to form the similar spiral state, the yarn stock 3 is twisted (twisting pitch P and waving pitch H) with the yarn stock 1 by forming of different pitch and waving height (forming pitch Pa and waving height Ha) to form a compounded spiral state (a, b), an open part X and a closed part Y are mutually formed in the longer direction of the cord and the forming pitch Pa of the yarn stock 3 is in the range of the formula when the diameter of the yarn stock 3 is (d) and twisting pitch is P.