A communication terminal includes a CPU (28). The CPU (28) issues to a router (16) a send request for requesting the router (16) to send an ask signal for repetitive responses to a server (14). Then, the ask signal is sent to the server (14) by the router (16), and a receive port is temporarily opened. From the server (14), a response signal is repeatedly sent in response to the ask signal. To the response signal, time information representative of a waiting time from receiving an ask signal to its reply is attached. A response signal sent back while the receive port is opened arrives at the communication terminal through the router (16), but a response signal sent back after the receive port is closed is discarded in the router (16). The CPU (28) repeatedly issues a send request to the router (16) regarding a time indicated by time information attached to the response signal lastly received as an issuance cycle (T).