A catheter of the present invention includes a tubular member and a lockable connector having a hub and a locking device. The locking device includes a semi-oval button; a rectangular main operating part; an accepting part having a pair of projections and an accepting hole; and a latching part coupled to one of the projections. The hub includes a guide hole into which the locking device is inserted and a first body passage formed horizontally toward the inside of the hub, the first body passage communicating with the guide hole. The locking device can be released from the locked position only by use of an appropriate key. A tip of the tubular member is made of hard material and has a double adhesion structure so that the catheter tube can easily be inserted into a body cavity.