A communication system comprising: a first external device; a second external device; a first communication device (20; 200; 201); and a second communication device (30; 300; 301), wherein the first communication device (20; 200; 201) includes a command prediction means (22; 220) and a first communication processing means (21; 210; 211), the command prediction means (22; 220) predicts an address and instruction content in a first command from a part of the first command having been input from the first external device, outputs to the first communication processing means (21; 210; 211), as a second command, the address and the instruction content having been predicted, and outputs first flag information indicating whether the second communication device needs to wait for transmission of the second command to the first communication processing means (21; 210; 211), the first communication processing means (21; 210; 211) transmits the second command and the first flag information to the second communication device, the second communication device (30; 300; 301) includes a second communication processing means (31; 310; 311), and the second communication processing means (31; 310; 311) receives the second command and the first flag information, and transmits the second command to the second external device when the first flag information indicates that the second communication device (30; 300; 301) does not need to wait for transmission of the second command, temporarily stops transmitting the second command to the second external device when the first flag information indicates that the second communication device (30; 300; 301) needs to wait for execution of the second command. a first external device; a second external device; a first communication device (20; 200; 201); and a second communication device (30; 300; 301), wherein the first communication device (20; 200; 201) includes a command prediction means (22; 220) and a first communication processing means (21; 210; 211), the command prediction means (22; 220) predicts an address and instruction content in a first command from a part of the first command having been input from the first external device, outputs to the first communication processing means (21; 210; 211), as a second command, the address and the instruction content having been predicted, and outputs first flag information indicating whether the second communication device needs to wait for transmission of the second command to the first communication processing means (21; 210; 211), the first communication processing means (21; 210; 211) transmits the second command and the first flag information to the second communication device, the second communication device (30; 300; 301) includes a second communication processing means (31; 310; 311), and the second communication processing means (31; 310; 311) receives the second command and the first flag information, and transmits the second command to the second external device when the first flag information indicates that the second communication device (30; 300; 301) does not need to wait for transmission of the second command, temporarily stops transmitting the second command to the second external device when the first flag information indicates that the second communication device (30; 300; 301) needs to wait for execution of the second command.