A first connector 2 is provided with: a first connector body composed of a cylindrical outer tube 4, a cylindrical inner tube 7, and a hub 12 a hollow needle 5 supported by the hub 12 a first sealing member supported by the inner tube 7 a coil spring 8 serving as a biasing means which biases the hub 12 in a proximal direction and also serving as a to-be-pierced section biasing means which biases the first sealing member in the distal direction and gripping and pressing members disposed on the outer tube 4. A plurality of pawls 126 are formed on a flange 124 of the hub 12. A plurality of ratchet teeth 41 are formed on the inner circumferential portion of a proximal portion of the outer tube 4. Each of the ratchet teeth 41 and each of the pawls 126 of the hub 12 form an engagement-disengagement mechanism 13.
