Elongation force (Ef) exerted by a seedling may be the most important factor for successful emergence under soil crust condition. In this paper, soybean seedling Ef was measured and its relations with seedling ethylene production and hypocotyl enlargement were investigated. The Ef exerted by a seedling increased dramatically with about 4 hours after setting the tip of seedling against the force receptor, then the Ef gave a gradual increase and reached a maximum after 36 to 48 hours although the seedling hypocotyls already bent after about 8 hours. In those seedlings which were used for the Ef test (elongation restriction), hypocotyl diameter became large from 8 to 12 hours after starting restriction. Further, in the same seedlings, ethylene production increased from 4 to 8 hours after starting restriction. When the evolved ethylene was removed by ethylene-acetaldehyde removing agent, hypocotyl thickness was reduced although it was still larger than that of unrestricted seedlings. The results suggested that, if the hypocotyl elongation is inhibited by soil particles or crust, the seedling ethylene production increases and the hypocotyl becomes thick, so that results the strong Ef to emerge.