An applicator for fitting a resilient rubber ring (22) around an elongated tube (20) of an endoscope includes a support device (11) having a through channel. A movable sleeve (14, 61, 84) is disposed through the through channel movably in forward and backward directions. Four arm devices (12, 46, 47, 63, 86) are arranged on a periphery of the movable sleeve, and kept pivotally movable on the movable sleeve between open and closed state positions. A receiving portion (12c, 46c, 63c, 86c) is disposed to extend from the arm device in the forward direction, for receiving the rubber ring outside. A shift mechanism (15, 50, 70, 82, 94) shifts the movable sleeve in the forward direction, and presses the arm devices with an end surface thereof to move pivotally from the closed state position to the open state position, so as to expand the rubber ring in a radial direction (A1) with the receiving portion. Finally, the rubber ring is advanced in the forward direction and set around the elongated tube.
