A robot system includes a robotic arm having a wrist in a tip-end part thereof, the wrist being rotatable on a rotational axis extending in a given direction, an end effector attached to the wrist, and a deformation detecting device configured to detect deformation of the end effector by using a target pin having a target part where a given detection part of the end effector reaches. The target part has an indicate function to indicate that the detection part reaches the target part. The deformation detecting device includes a search part configured to control the robotic arm so that the detection part touches the target pin to search for the target part, and detect that the detection part reaches the target part based on the indicate function, and a deformation detecting part configured to compare an assumed position of the detection part when the detection part reaches the target part with a given reference position, and detect the deformation of the end effector.