To transmit a signal and information for control and maintenance required for data transmission without disturbing major transmission being data transmission.

The control signal transmitter is provided with a data transmitter of a configuration to send a main signal being a major transmission object where a transmission processing unit 102 transmits a main signal being a major transmission object via a main signal highway and a line connection unit 103 according to an instruction from a control unit 101. The control signal transmitter transmits a control signal and control information and maintenance information required for the transmission of the main signal is also provided with a control signal transmission means 111 that intervenes transmission of the control signal via a control signal highway provided between the control unit 101 and the line connection unit 103, an insert means 112 that inserts the control information and the maintenance information to a prescribed time slot on the control signal highway, and an extract means 113 that extracts the control information and the maintenance information to be sent to the transmission processing unit in prescribed time slot of the control signal highway.