A treatment instrument system according to the present invention includes: an endoscope having a treatment instrument channel; an ultrasound probe inserted through the treatment instrument channel of the endoscope; an ultrasound observing apparatus having a blood flow display function and a distance measuring function; a treatment instrument having, at a distal end portion, an ultrasound scattering portion for scattering ultrasound; and an over tube having an endoscope insertion path through which the endoscope can be inserted and a treatment instrument insertion path through which the treatment instrument can be inserted, and having, at a distal end portion, an ultrasound scattering portion for scattering ultrasound.