The fixed valve and the attachable and detachable valve are connected to each other via a connecting band, and both are integrally made of elastomer. A frame body is constituted of a rigid body made of plastic. A flange and a receiving portion are formed on an upper portion of the frame body. A second flange is formed on a lower end of the fixed valve. The fixed valve is installed on the frame body by engaging the second flange with flange. The second flange is prevented from being separated from the flange of the second flange by interposing a part of the second flange between the flange and the receiving portion. The fixed valve is securely installed on the frame body, whereby the fixed valve is prevented from uncoupling when removing a treatment tool.
