An endoscope system includes: an endoscope having a field of view in front of a distal end portion of an insertion portion an insertion assisting instrument including a conduit having an inner portion through which the insertion portion can be inserted and an angle operation portion that varies an angle of a distal end portion of the conduit an image generation section that generates an image corresponding to the field of view of the endoscope a rotation angle calculation section that calculates a rotation angle indicating to what extent the insertion portion inserted through the inner portion of the conduit is rotated with respect to the insertion assisting instrument, based on the image generated by the image generation section and an image rotation section that rotates the image so as to display the image, with the rotation angle being offset.
