PROBLEM TO BE SOLVED: To provide a catheter auxiliary device which can easily solve the problem of a blood removal failure, and a catheter set for dialysis using the catheter auxiliary device.SOLUTION: The device 50 includes: a connector 20 a shaft 13 which can be inserted into/extracted from the blood removal lumen 110 of a catheter 100 via the connector 20 a capture part 11 which can be projected from a blood removal opening part 111 a body part 10 at least constituted of the shaft 13 and the capture part 11 and an adapter 30 which supports the body part 10 so as to be insertable while tightly closing the lumen of the connector 20. Thus, in a state that the inside of the lumen of the catheter 100 and the lumen of the connector 20 are made negative pressure by a negative pressure generator, the shaft 13 can be inserted/extracted into/from the blood removal lumen 110.
