Historically speaking, building a bridge between Honshu and Shikoku was proposed quite early; first in 1889 and then in 1940. By the recent serious marine accident, the need for the bridge became greater. The bridge takes on importance firstly in the activation of Kinki, Chugoku, and Shikoku; secondly in the convenience of transportation and thirdly in the prevention of marine accidents. The technique of building a long-big bridge is compared by its length. As for Seto Ohashi, with the length of 940m, the technique is on the top level in the world. Since the wind has strong effects on long-big bridges, wind-tunnel tests and simulation techniques are used freely to solve the problems. A bridge with a railroad, like Seto Ohasi, bears a load twice as heavy as a bridge only with a road. And welding, techniques at the construction site, and devices and quality control are especially to be considered.