A medical instrument for treating sinusitis has a body, an insert tube extending from a distal end of the body, and an angle portion extending from a distal end of the insert tube. The angle portion is bent by a remote control member mounted on the body, through a wire. A motor is mounted on the body. The medical instrument also has a brush. This brush has an elongated rotation transmission portion extending through the insert tube and the angle tube, and a brush portion attached to a distal end of the rotation transmission portion. A basal portion of the rotation transmission portion is connected to the motor. The brush portion is allowed to protect from a distal end of the angle tube. At least that portion of the rotation transmission portion extending through the angle tube is bendable. Therefore, when the motor is rotated in the state that the angle portion is bent, the brush portion is rotated.