1. A medical apparatus system comprising: a medical apparatus including an observing section having an objective lens having an observation field of view; an image generating section configured to generate a first image of an inside of the observation field of view obtained from the observing section; a treatment instrument used together with the medical apparatus, at least a proximal end side of the treatment instrument being arranged on an outside of the observation field of view of the observing section; an information collecting section that collects information including at least a position and direction on a distal end side of the treatment instrument; an outside-of-observation-field-of-view computer graphic image generating section configured to generate a computer graphic image of the treatment instrument on at least the outside of the observation field of view using the information collected by the information collecting section; an outside-of-observation-field-of-view distortion setting section that sets virtual distortion for the computer graphic image of the treatment instrument on the outside of the observation field of view on the basis of information on a characteristic of distortion of the objective lens; an outside-of-observation-field-of-view distorted image generating section that generates at least a three-dimensional or two-dimensional distorted image as a second image obtained by virtually distorting the computer graphic image of the treatment instrument on the outside of the observation field of view on the basis of the information collected by the information collecting section and the virtual distortion set by the outside-of-observation-field-of-view distortion setting section; and an image combining section configured to generate, when the distal end side of the treatment instrument is captured on the inside of the observation field of view, a combined image which includes the first image of the treatment instrument on the inside of the observation field of view and the second image obtained by distorting the treatment instrument on the outside of the observation field of view, and in which the first image and the second image coincide with each other in a boundary of the observation field of view.