Disclosed is a one cord blind that has a simplified structure enabling it to be easily manufactured, prevents a safety accident by not using a ball chain, makes an interior design neat and enables a roll screen to move upward and downward by a rotating cord or hands, so that the upward and downward operations can be easily made. The steel part includes steel having a composition containing 0. In an embodiment, the boss, in addition to being posteriorly offset, is superiorly offset from the central bore by at least 8 mm.