Information terminal apparatus, information processing apparatus and information communication system

When transmitting position/time information calculated by means of a GPS function to a server apparatus, authentication is carried out with the server apparatus. The position/time information may be certified as legitimate measured by a portable apparatus with a GPS reception function employed by a user. When transmitting information related to the position and the time acquired from a portable phone terminal having the GPS function and a network function by means of the GPS function to the server apparatus, authentication is carried out between the portable phone terminal and the server apparatus. The position/time information is transmitted to the server apparatus, only if the server apparatus is authenticated as a legitimate counterpart for connection. A secret key holding section is provided for holding different secret keys for different apparatuses. The position/time information measured based on an electromagnetic wave received from a positioning satellite is digitally signed by means of the secret key. The identification information and the position/time information having the digital signature are then transmitted to a counterpart.