Communication system having group accession function

The invention provides a communication system with a group registration function, which is capable of setting a group mode with the reduced number of operation, and simply selecting one of full duplex communication and half duplex communication by a rider, as needed. To achieve this, in a communication system with a group registration function, when a power supply SW (switch) and a registration SW are turned on simultaneously (answer in step S1 is affirmed), member ID registration is executed (step S7). On the other hand, when the power supply SW is turned on and then the registration SW is turned on (answer in step S3 is affirmed), visitor ID registration is executed (step S8). Accordingly, the registration of a group mode can be simplified. After the registration is ended, at the time of turn-off of a visitor conversation SW, full duplex communication is performed among communication devices subjected to member ID registration, and at the time of turn-on of the visitor conversation SW, half duplex communication is performed between the master and all of the slaves.