During a robot is taking workpieces out of a workpiece container 2, a safety fence 2 and a photoelectric sensor 1 are valid and the robot is stopped when the safety fence 2 is opened or a beam from the photoelectric sensor 1 is cut off. A safety fence 1 and a photoelectric sensor 2 are invalid and do not hinder operation of the robot. Operation feasible state indicating lamps of workpiece feeding lamp/switch boxes 1 and 2 are turned on and off, respectively. If an operator replaces a workpiece container 1, he/she actuates an operating area entrance switch or the box 1 into an ON state to make OFF state an operation feasible signal for the robot RB on a side of the workpiece container 1. When the robot is operating on the side of the workpiece container 1, the robot can continue to operate while similarly ensuring safety of the operator.