1. A robot controller controlling a robot, the robot performing loading and unloading of a workpiece relative to a plurality of machine tools controlled by a plurality of machine tool controllers, respectively, wherein the plurality of machine tool controllers are disposed separately from the robot controller and do not control the robot, each machine tool controller configured to control operation of the corresponding machine tool; wherein the robot controller is connected to a portable teach pendant used for operating the robot controller, and is also connected to the plurality of machine tool controllers through a communication network; wherein said teach pendant comprises a display section configured to display information of the plurality of machine tools; wherein said robot controller is configured to obtain information of the plurality of machine tools from the corresponding machine tool controllers through said communication network, make said display section of said teach pendant display a machine tool-related screen including a CNC selection button, and make said machine tool-related screen of said display section of said teach pendant display the information of the plurality of machine tools, such that a machine tool controller of the plurality of the machine tool controllers can be selected by the CNC selection button displayed on the display section of the teach pendant, and information of the selected machine tool corresponding to the selected machine tool controller is presented in the teach pendant display; wherein, when an input operation is performed on said machine tool-related screen of said display section of said teach pendant, said robot controller is configured to transmit a content of said input operation to the selected machine tool controller through said communication network; and wherein said robot controller is configured to enable the selected machine tool controller to be operated by said input operation performed on said machine tool-related screen.