A circuit for collecting a blood component includes a blood collection device provided with a blood collection needle through which blood is collected from a blood donor, a blood separator in which the blood collected by the above blood collection device is separated, a blood component collection bag in which a predetermined blood component separated by the above blood separator is collected, a blood line in which the blood collection needle is connected to an inlet of the blood separator, a line for removing an initial blood flow, which branches from a first branching portion formed in the blood line, and in which an initial flow of blood collected from the blood donor is removed, and an anticoagulant-injection line that branches from a second branching portion, formed in the line for removing the initial blood flow, and into which an anticoagulant is injected.