A device and a method for automatically setting an interlock based on a suitable interference area obtained by executing an offline simulation in relation to a system including a plurality of robots. The device executes the simulation on the offline programming system based on a motion program so as to determine a moving path of the robots and a two-dimensional interference area between the robots. Next, the device calculates a first three-dimensional interference area by moving the two-dimensional area in the vertical direction and calculates an accurate second three-dimensional interference area within the first interference area, using three-dimensional models of the robots.