Data formulated according to a user's request signal is transmitted from a transmitter device to a receiver device under a wireless or a wired system. The transmitter device includes a transmission controller that formulates the data to be transmitted and memorizes the request signal as a backup signal. If the data transmission is not completed due to a power source trouble such as a voltage drop, the data to be transmitted is automatically formulated again based on the backup signal and sent out to the receiver. If the data transmission is successful, the backup signal is eliminated from a memory. Thus, the data requested by the user is transmitted without fail even if the transmitter becomes temporarily inoperative.