A blood circuit connector comprising; a main body having a cylindrical shape, the main body having a through hole provided therein to have one end provided with a first opening end and the other end provided with a second opening end; a plug having a bottomed cylindrical shape and detachably attached to the first opening end; and a connection part having flexibility and configured to connect the main body and the plug, the plug including a side wall loosely fitted to an outer circumferential surface of the first opening end and a bottom facing the first opening end in an extending direction of an axis line of the main body in an attached state where the plug is attached to the first opening end, the connection part including a first fixed end connected to the side wall of the plug, a second fixed end connected to an outer circumferential surface of the main body, wherein the second fixed end includes a linear-shaped inclined part that is inclined in a direction away from the main body characterized in that the connection part includes a curved part located between the first fixed end and the linear-shaped inclined part, and expanding in a direction away from the main body, in the attached state, the curved part being pushed in a direction approaching the outer circumferential surface of the main body such that the curved part extends, to cancel a loosely fitted state between the side wall of the plug and the outer circumferential surface of the first opening end, so as to remove the plug from the first opening end, wherein the connection part further includes an elastic force generating part having an S-shape located between the first fixed end and the curved part, and flexibly deformed in the attached state so as to generate elastic force, the plug is attached to the first opening end as the plug swings against the elastic force generated by the elastic force generating part such that an axis line of the plug extends in line with the axis line of the main body, and when the plug is removed, the loosely fitted state between the side wall of the plug and the outer circumferential surface of the first opening end is cancelled, to cause the plug to swing with restoring force produced based on the elastic force generated by the elastic force generating part, so as to move the plug away from above the axis line of the main body. a main body having a cylindrical shape, the main body having a through hole provided therein to have one end provided with a first opening end and the other end provided with a second opening end; a plug having a bottomed cylindrical shape and detachably attached to the first opening end; and a connection part having flexibility and configured to connect the main body and the plug, the plug including a side wall loosely fitted to an outer circumferential surface of the first opening end and a bottom facing the first opening end in an extending direction of an axis line of the main body in an attached state where the plug is attached to the first opening end, the connection part including a first fixed end connected to the side wall of the plug, a second fixed end connected to an outer circumferential surface of the main body, wherein the second fixed end includes a linear-shaped inclined part that is inclined in a direction away from the main body characterized in that the connection part includes a curved part located between the first fixed end and the linear-shaped inclined part, and expanding in a direction away from the main body, in the attached state, the curved part being pushed in a direction approaching the outer circumferential surface of the main body such that the curved part extends, to cancel a loosely fitted state between the side wall of the plug and the outer circumferential surface of the first opening end, so as to remove the plug from the first opening end, wherein the connection part further includes an elastic force generating part having an S-shape located between the first fixed end and the curved part, and flexibly deformed in the attached state so as to generate elastic force, the plug is attached to the first opening end as the plug swings against the elastic force generated by the elastic force generating part such that an axis line of the plug extends in line with the axis line of the main body, and when the plug is removed, the loosely fitted state between the side wall of the plug and the outer circumferential surface of the first opening end is cancelled, to cause the plug to swing with restoring force produced based on the elastic force generated by the elastic force generating part, so as to move the plug away from above the axis line of the main body.