A communication system, comprising a master machine and a slave machine that is controlled by the master machine, which are configured to communicate with each other, the master machine includes a copy instruction transmission module configured to transmit a copy instruction to the slave machine, and the communication system being characterized in that the slave machine includes: a data storage that includes a first storage area and a second storage area; an update module configured to repeatedly update data in the first storage area based on operation of the slave machine, the data being a state of the slave machine and the first storage area being updated when an operation command from the master machine is executed; a copy module configured to copy the data in the first storage area to the second storage area when the copy instruction is received, wherein the copy module does not copy the data in the first storage area to the second storage area when the copy instruction is not received and postpones the copy of the data in the first storage area until the copy instruction is received, the second storage area not being updated when the operation command is executed; and a transmission module configured to transmit the data in the second storage area to the master machine when a data request is received from the master machine, wherein the transmission module does not transmit the data in the second storage area to the master machine and postpones the transmitting of the data when the data request is not received from the master machine. the master machine includes a copy instruction transmission module configured to transmit a copy instruction to the slave machine, and the communication system being characterized in that the slave machine includes: a data storage that includes a first storage area and a second storage area; an update module configured to repeatedly update data in the first storage area based on operation of the slave machine, the data being a state of the slave machine and the first storage area being updated when an operation command from the master machine is executed; a copy module configured to copy the data in the first storage area to the second storage area when the copy instruction is received, wherein the copy module does not copy the data in the first storage area to the second storage area when the copy instruction is not received and postpones the copy of the data in the first storage area until the copy instruction is received, the second storage area not being updated when the operation command is executed; and a transmission module configured to transmit the data in the second storage area to the master machine when a data request is received from the master machine, wherein the transmission module does not transmit the data in the second storage area to the master machine and postpones the transmitting of the data when the data request is not received from the master machine. a data storage that includes a first storage area and a second storage area; an update module configured to repeatedly update data in the first storage area based on operation of the slave machine, the data being a state of the slave machine and the first storage area being updated when an operation command from the master machine is executed; a copy module configured to copy the data in the first storage area to the second storage area when the copy instruction is received, wherein the copy module does not copy the data in the first storage area to the second storage area when the copy instruction is not received and postpones the copy of the data in the first storage area until the copy instruction is received, the second storage area not being updated when the operation command is executed; and a transmission module configured to transmit the data in the second storage area to the master machine when a data request is received from the master machine, wherein the transmission module does not transmit the data in the second storage area to the master machine and postpones the transmitting of the data when the data request is not received from the master machine.