Provided is a data communication system comprising : a wireless communication internet terminal connected to a wireless communication network; and a server, on the Internet, for providing a specific service, wherein while the specific service is being provided, the communication quality of the wireless communication network can be easily ascertained so as to make it possible to address a network fault promptly. A wireless tablet terminal 11 acquires customer information data concerning a customer visiting an exhibition booth or the like at a trade fair, and transmits the customer information data to an application server 31, and at the same time, also records and transmits transmission history information of the customer information data. The application server 31 compiles the transmission history information, in addition to the customer information, into a database, and monitors the communication quality of a wireless communication network 41 through analysis of the received transmission history information, and, upon detecting an aberration therein, transmits a warning mail to an electronic mail address of a network administrator or the like.