A tube connector configured to connect between a main tube comprising a flexible tubular member and a peristaltically-actuated tube comprising a flexible tubular member and being configured to be squeezed in a longitudinal direction while being compressed in a radial direction by a squeezing part to make blood flow therethrough, the tube connector comprising: a first connection part 1 configured to be connected to the main tube ; a second connection part configured to be connected to the peristaltically-actuated tube ; a communication part being provided between the first connection part and the second connection part and having a communication flow path for communicating between a first flow path through which fluid flows in the first connection part and a second flow path through which the fluid flows in the second connection part ; and a main body section being constituted by sequentially providing the first connection part, the communication part, and the second connection part in an axial direction of the main body section , wherein the first flow path and the second flow path are formed to have a constant diameter and are formed so as to extend along the axial direction of the main body section , wherein a diameter of the first flow path is smaller than a diameter of the second flow path, wherein the communication flow path is formed so as to gradually enlarge in diameter from a first flow path side to a second flow path side, wherein a central axis of the first flow path and a central axis of the second flow path are shifted toward the radial direction of the main body section ; wherein the central axis of the first flow path is shifted upward in use state with respect to the central axis of the second flow path; wherein an inner diameter of the main tube is smaller than an inner diameter of the peristaltically-actuated tube ; and wherein the main tube and the peristaltically-actuated tube are for extracorporeal circulation of the blood of a patient. a first connection part 1 configured to be connected to the main tube ; a second connection part configured to be connected to the peristaltically-actuated tube ; a communication part being provided between the first connection part and the second connection part and having a communication flow path for communicating between a first flow path through which fluid flows in the first connection part and a second flow path through which the fluid flows in the second connection part ; and a main body section being constituted by sequentially providing the first connection part, the communication part, and the second connection part in an axial direction of the main body section , wherein the first flow path and the second flow path are formed to have a constant diameter and are formed so as to extend along the axial direction of the main body section , wherein a diameter of the first flow path is smaller than a diameter of the second flow path, wherein the communication flow path is formed so as to gradually enlarge in diameter from a first flow path side to a second flow path side, wherein a central axis of the first flow path and a central axis of the second flow path are shifted toward the radial direction of the main body section ; wherein the central axis of the first flow path is shifted upward in use state with respect to the central axis of the second flow path; wherein an inner diameter of the main tube is smaller than an inner diameter of the peristaltically-actuated tube ; and wherein the main tube and the peristaltically-actuated tube are for extracorporeal circulation of the blood of a patient. <EOS>