A motion limiting device comprising: detection means configured to detect environmental information around a robot, wherein the robot comprises operation means for operating an operation target object and moving means for moving the robot; generation means (62, 621) configured to generate, based on the environmental information detected by the detection means, a three-dimensional environment model that includes an unobservable area and an observable area and indicates a working environment in which the robot operates, the unobservable area being the area where the environmental information cannot be detected by the detection means, and the observable area being the area where the environmental information can be detected by the detection means; and limiting means (62, 622) configured to limit a motion of the robot when it is determined that the robot has entered the unobservable area by limiting at least one of a motion speed, a motion acceleration, and an operational force of the robot, characterized in that upon determining that the robot has entered the unobservable area based on the three-dimensional environment model generated by the generation means, the limiting means (62, 622) is configured to decrease a motion speed limit value that determines an upper limit of the motion speed of the moving means and the operation means and an operational force limit value that determines an upper limit of the operational force of the moving means and the operation means, upon determining that the robot is within a predetermined distance from the unobservable area and moves in a direction of the unobservable area based on the environmental information detected by the detection means and the three-dimensional environment model generated by the generation means, the limiting means (62, 622) is configured to gradually decrease the motion speed limit value and the operational force limit value, as the distance between the robot and the unobservable area decreases, and the generation means (62, 621) is configured to change, in the three-dimensional environment model, an area in the unobservable area, where the robot has operated before, to the observable area, and to keep, in the three-dimensional environment model, an area in the observable area, which becomes an unobservable area when the robot enters the observable area, as the observable area. detection means configured to detect environmental information around a robot, wherein the robot comprises operation means for operating an operation target object and moving means for moving the robot; generation means (62, 621) configured to generate, based on the environmental information detected by the detection means, a three-dimensional environment model that includes an unobservable area and an observable area and indicates a working environment in which the robot operates, the unobservable area being the area where the environmental information cannot be detected by the detection means, and the observable area being the area where the environmental information can be detected by the detection means; and limiting means (62, 622) configured to limit a motion of the robot when it is determined that the robot has entered the unobservable area by limiting at least one of a motion speed, a motion acceleration, and an operational force of the robot, characterized in that upon determining that the robot has entered the unobservable area based on the three-dimensional environment model generated by the generation means, the limiting means (62, 622) is configured to decrease a motion speed limit value that determines an upper limit of the motion speed of the moving means and the operation means and an operational force limit value that determines an upper limit of the operational force of the moving means and the operation means, upon determining that the robot is within a predetermined distance from the unobservable area and moves in a direction of the unobservable area based on the environmental information detected by the detection means and the three-dimensional environment model generated by the generation means, the limiting means (62, 622) is configured to gradually decrease the motion speed limit value and the operational force limit value, as the distance between the robot and the unobservable area decreases, and the generation means (62, 621) is configured to change, in the three-dimensional environment model, an area in the unobservable area, where the robot has operated before, to the observable area, and to keep, in the three-dimensional environment model, an area in the observable area, which becomes an unobservable area when the robot enters the observable area, as the observable area.