Provided are an interleaving apparatus for improving transmission performance and an interleaving method used by the interleaving apparatus. The interleaving apparatus determines the type of data at each element position of an interleaving matrix, reads encoded data, which corresponds to the determined type of data at each element position, from an encoder, rearranges the read data in an order determined by the interleaving matrix, and outputs the rearranged data. Since the interleaving apparatus does not include a memory, it can prevent delay in signal processing, thereby improving transmission performance.