An information processing terminal system includes an information processing terminal (6); and a transmitting and receiving unit (5) which is attached to the information processing terminal. The transmitting and receiving unit (5) converts a reception wave signal from a network into a reception analog baseband signal. The transmitting and receiving unit (5) converts the reception analog baseband signal into a reception digital baseband signal in synchronization with a clock. The information processing terminal (6) converts the reception digital baseband signal into a reception data in synchronization with a clock, and a transmission data into a transmission digital baseband signal in synchronization with the clock. The transmitting and receiving unit (5) converts the transmission digital baseband signal into a transmission analog baseband signal in synchronization with the clock. The transmitting and receiving unit (5) converts the transmission analog baseband signal into a transmission modulation wave signal to output to the network.