In a contents data transmission/reception system, a contents data transmitter generates a plurality of key information, encrypts contents data by using one of the key information, transmits the key information through a plurality of signal routes to a contents data receiver, and then, transmits the encrypted contents data used by the key information through the signal routes to the contents data receiver. The contents data receiver receives the key information and the encrypted contents data transmitted from the contents data transmitter through the signal routes, and decrypts the encrypted contents data by using the key information.