A robot simulation device, capable of simulating if a robot can transfer an object without any interference in a working space where obstacles are disposed. The device comprises of an input device, a display, a processing unit, computing programs and an output device of teaching programs. And the device further comprises of: (1) a two-dimensional display part having coordinate axes, (2) a means of displaying the obstacles and working space, a means of displaying a path of the moving robot, and a means of displaying the transferred object by the robot, on the display, (3) a means of interpolating the path by designating moving points of a central point of the moving transferred object, (4) a means of displaying the path of the moving transferred object in the working space, and (5) a means of displaying a region where the path interferes with the obstacles.