A control system having device units removably attachable to a control device such as a computer is arranged to optimize the allocation and distribution of electric power to the device units and also displays of varied kinds. For this purpose, each device unit of the system includes a communication circuit arranged to transmit information of electric power consumption and an operating state of the device unit detachably connected to the control device such as a computer, a stopping circuit for partly stopping a function of the device unit according to a control signal sent in reply from the control device on the basis of information of varied kinds transmitted through the transmission circuit to the control device. The control device, on the other hand, includes a communication circuit arranged to receive the information on the device unit from the device unit, and a control circuit arranged to compare the information of electric power consumption and the operating state received by the communication circuit with information of the amount of electric power which can be supplied to the device unit and to send the control signal to the device unit for partly stopping the function of the device unit according to the result of comparison. Further, the control device changes a display made therein and controls the operation of the device unit according to information of the operating state and the connected state of the device unit.