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.