A medical treatment device inserted into a treatment instrument insertion channel of an ultrasonic endoscope inserted into a body cavity for treating an organ in the body cavity comprises a treatment probe having an electrode portion inserted and stuck into the organ in the body cavity through the treatment instrument insertion channel of the ultrasonic endoscope for radio-frequency cautery treatment of a tissue in the organ and an ultrasonic reflection portion formed on the surface of the electrode portion of the treatment probe for reflecting an ultrasonic signal from the ultrasonic endoscope.
