A control system comprises: a controller configured to generate a control frame and to transmit the control frame to slave devices (21, 22, 23); the control system is characterized in that further comprising: a loopback communication device configured to perform loopback communication of the control frame and having the same hardware configuration as the controller; a first communication route to which the slave devices are connected using a first communication cable (31, 32, 33, 34) between the controller and the loopback communication device; and a second communication route to which the controller and the loopback communication device are connected through a second communication cable, wherein the controller includes a first transception part configured to transmit and receive the control frame to and from the first communication route and the second communication route, when one of the slave devices (21, 22, 23) connected and placed directly downwards to the controller up to a disconnection performs loopback communication of the control frame to the controller via the first communication route, the first transception part is configured to analyze the control frame received from the first communication route to determine whether or not the control frame has not passed through all of the slave devices (21, 22, 23) connected to the first communication route because of the disconnection in the first communication cable (31, 32, 33, 34) based on a presence or absence of a time stamp in each of the slave devices (21, 22, 23), and the first transception part is configured to transmit the control frame to the loopback communication device via the second communication route when there is the absence of the time stamp in one of the slave devices (21, 22, 23) downwards of the disconnection, and the loopback communication device is configured to receive the control frame transmitted by the first transception part via the second communication route, and to transmit the received control frame to one of the slave devices (21, 22, 23) downwards of the disconnection and connected to the loopback communication device, wherein the one of the slave devices (21, 22, 23) downwards of the disconnection performs loopback communication of the control frame to the loopback communication device configured to perform loopback communication of the control frame to the controller via the second communication route, wherein the loopback communication device includes a second transception part configured to transmit and receive the control frame to and from the first communication route and the second communication route. a loopback communication device configured to perform loopback communication of the control frame and having the same hardware configuration as the controller; a first communication route to which the slave devices are connected using a first communication cable (31, 32, 33, 34) between the controller and the loopback communication device; and a second communication route to which the controller and the loopback communication device are connected through a second communication cable, wherein the controller includes a first transception part configured to transmit and receive the control frame to and from the first communication route and the second communication route, when one of the slave devices (21, 22, 23) connected and placed directly downwards to the controller up to a disconnection performs loopback communication of the control frame to the controller via the first communication route, the first transception part is configured to analyze the control frame received from the first communication route to determine whether or not the control frame has not passed through all of the slave devices (21, 22, 23) connected to the first communication route because of the disconnection in the first communication cable (31, 32, 33, 34) based on a presence or absence of a time stamp in each of the slave devices (21, 22, 23), and the first transception part is configured to transmit the control frame to the loopback communication device via the second communication route when there is the absence of the time stamp in one of the slave devices (21, 22, 23) downwards of the disconnection, and the loopback communication device is configured to receive the control frame transmitted by the first transception part via the second communication route, and to transmit the received control frame to one of the slave devices (21, 22, 23) downwards of the disconnection and connected to the loopback communication device, wherein the one of the slave devices (21, 22, 23) downwards of the disconnection performs loopback communication of the control frame to the loopback communication device configured to perform loopback communication of the control frame to the controller via the second communication route, wherein the loopback communication device includes a second transception part configured to transmit and receive the control frame to and from the first communication route and the second communication route.