A communication system comprising: a first communication device configured to carry out wireless communication; and a second communication device configured to carry out wireless communication; wherein the first communication device includes setting means for setting an initiator indication mode and a target indication mode corresponding to the initiator indication mode, sending means for sending data representing the target indication mode to the second communication device when communication has been established with the second communication device, key exchanging means for securely exchanging a communication key with the second communication device, and first indicating means for indicating the establishment of communication between the first communication device and the second communication device in the initiator indication mode, correspondingly to indication of the establishment of communication in the target indication mode by the second communication device; and wherein the second communication device includes receiving means for receiving the data representing the target indication mode, the data having been sent from the first communication device, and second indicating means for indicating the establishment of communication between the first communication device and the second communication device in the target indication mode, correspondingly to the indication of the establishment of communication in the initiator indication mode by the first communication device; wherein the communication means of the first communication device is arranged to send the data representing the target indication mode to the second communication device after completion of the exchange of the communication key, the data being sent in an encrypted form using the communication key; characterized in that the setting means of the first communication device is arranged to use a random number to determine what content is to be generated, in the initiator and target indication modes, to indicate establishment of communication between the first communication device and second communication device. a first communication device configured to carry out wireless communication; and a second communication device configured to carry out wireless communication; wherein the first communication device includes setting means for setting an initiator indication mode and a target indication mode corresponding to the initiator indication mode, sending means for sending data representing the target indication mode to the second communication device when communication has been established with the second communication device, key exchanging means for securely exchanging a communication key with the second communication device, and first indicating means for indicating the establishment of communication between the first communication device and the second communication device in the initiator indication mode, correspondingly to indication of the establishment of communication in the target indication mode by the second communication device; and setting means for setting an initiator indication mode and a target indication mode corresponding to the initiator indication mode, sending means for sending data representing the target indication mode to the second communication device when communication has been established with the second communication device, key exchanging means for securely exchanging a communication key with the second communication device, and first indicating means for indicating the establishment of communication between the first communication device and the second communication device in the initiator indication mode, correspondingly to indication of the establishment of communication in the target indication mode by the second communication device; and wherein the second communication device includes receiving means for receiving the data representing the target indication mode, the data having been sent from the first communication device, and second indicating means for indicating the establishment of communication between the first communication device and the second communication device in the target indication mode, correspondingly to the indication of the establishment of communication in the initiator indication mode by the first communication device; receiving means for receiving the data representing the target indication mode, the data having been sent from the first communication device, and second indicating means for indicating the establishment of communication between the first communication device and the second communication device in the target indication mode, correspondingly to the indication of the establishment of communication in the initiator indication mode by the first communication device; wherein the communication means of the first communication device is arranged to send the data representing the target indication mode to the second communication device after completion of the exchange of the communication key, the data being sent in an encrypted form using the communication key; characterized in that the setting means of the first communication device is arranged to use a random number to determine what content is to be generated, in the initiator and target indication modes, to indicate establishment of communication between the first communication device and second communication device.