In the case of rotating a slave unit(4) by operating a master apparatus(2), in order to maintain a correspondence relation between a position of the master apparatus(2) and a position of treatment tools(9) on a monitor screen, there is provided a master-slave system (1) including: a slave unit(4) including an observation optical system(8) imaging a subject A a treatment part(9) projecting from a surface(3a) on which the observation optical system(8) is provided and at least part of the treatment tools(9) is imaged along with the subject A by the observation optical system(8) a master apparatus(2) including an operating unit(23) held and operated by an operator a control unit associating operation of the operating unit(23) of the master apparatus 2 with motion of the slave unit(4) and motion of the treatment part(9) and a monitor screen displaying an image acquired by the observation optical system(8), wherein the operating unit(23) includes a command input unit(25) into which a motion command for a slave unit(2) is inputted while the operating unit(23) is held by the operator without changing a pose of the operating unit (23).
