An ultrasonic transmitter unit includes: a sheath that forms a cylindrical shape and is having a proximal end and a distal end; an ultrasonic transmitter configured to be inserted into the sheath; and a cover member that covers a part of the ultrasonic transmitter and has an inner surface and an outer surface. The ultrasonic transmitter includes: a first area surrounded by the sheath; a second area protruding from the distal end of the sheath; and a distal-end treatment portion provided in a distal end of the second area. The cover member covers the second area of the ultrasonic transmitter, and exposes the distal-end treatment portion of the ultrasonic transmitter to an outside, and is made of fluorine-based resin.