A communication system constituted with a portable phone, a hot spot computer, and a server unit establishing radio communication is provided. The portable phone includes a circuit receiving identification information from the hot spot computer, which is a party on the other end in radio communication; a circuit transmitting the received identification information to the server unit; a circuit receiving authentication information of a computer corresponding the identification information transmitted to the server unit; and a circuit transmitting connection request information along with the authentication information received from the server unit to the hot spot computer. The hot spot computer includes a circuit permitting communication with the portable phone based on whether or not the authentication information obtained by the portable phone matches the authentication information stored in advance in the hot spot computer, in response to receiving of the connection request information.