This robot system is equipped with: a screw-driving mechanism (1) that has a holding shaft (11) with a leading end formed in a shape complementary to the head (8a) of an external thread (8) so that when engaged with the head of the external thread, the positional relation with the external thread about the axis of the external thread is fixed, and a holding shaft drive unit (13) rotatively driving the holding shaft about the axis of the holding shaft; a robot body (2) that holds and moves the screw-driving mechanism; and a robot controller (3) that controls the robot body and controls the holding shaft drive unit as an external shaft which performs work in cooperation with the robot body.
