A robot control unit (30) comprises: a setting means (40) for setting operating ranges of each shaft and a working tool of the robot (20); a storage means (33) for storing an inertial running distance of the robot decided by at least one of the operating speed of the robot and the weight of the working tool; and an arriving range calculation means (36) for calculating an arriving range to which the robot arrives according to the operating range, which has been set by the setting means, and the inertial running distance stored by the storage means. Due to the foregoing, while consideration is being given to the inertial running distance of a robot, the arriving range of the robot is made. Further, a display means (41) for displaying the arriving range may be provided. In the case where each shaft of the robot and the working tool deviate from the operating range, a stopping means (34) for stopping the robot may be provided.