An antenna apparatus which ensures a wide reading area on a reader antenna and a reading operability of information recorded in a small-sized radio frequency IC tag is provided. The apparatus includes an auxiliary antenna of .lamda./2 long disposed near to a radiating antenna of .lamda./2 long and including plural conductive elements in an array. When the IC tag approaches the auxiliary antenna, a subsidiary tuning circuit is formed between it and an inlet antenna of IC tag, so making tuning complementary to each other. The inlet antenna having an antenna length shorter than the tuning frequency can receive energy from the auxiliary antenna efficiently and is excited integrally with the auxiliary antenna to thereby spread a reading area by apparatus and increase the communication distance.