A robot system includes a first conveyor, a second conveyor, a robot, and a controller. The first conveyor conveys a plurality of kinds of workpieces. The second conveyor conveys workpiece groups each including a combination of the workpieces. The controller controls the robot, and includes a situation acquirer, a determiner, and an instructor. The situation acquirer acquires a situation in a predetermined monitor area on the first and second conveyors. The monitor area is set based on a movable range of the robot. Based on the situation, the determiner determines whether one of the workpieces on the first conveyor in the monitor area is a missing workpiece of one of the workpiece groups in the monitor area. The instructor instructs the robot to hold the one workpiece and to transfer the one workpiece from the first conveyor to the second conveyor.