A master-slave system including: a slave device that includes an observation optical system and a treatment portion that protrudes from a surface on which the observation optical system is provided； a master device that includes a handle that is supported so as to be capable of rotating about a predetermined axis and a treatment manipulation portion； a control portion that associates rotation of the handle with rotation of the slave device about an axis intersecting the surface and that associates manipulation of the treatment manipulation portion with movement of the treatment portion； an image processing portion that generates a corrected image obtained by rotating an image of a subject and the treatment portion acquired by the observation optical system by a rotation angle of the slave device； and a monitor that displays the corrected image.
