A transmitting apparatus and a receiving apparatus are provided. The transmitting apparatus includes: an encoder configured to generate a low density parity check (LDPC) codeword by performing LDPC encoding; an interleaver configured to interleave the LDPC codeword; and a modulator configured to modulate the interleaved LDPC codeword according to a modulation method to generate a modulation symbol. The interleaver is formed of a plurality of columns each including a plurality of rows and includes a block interleaver configured to divide each of the plurality of columns into a first part and a second part and interleave the LDPC codeword, the number of rows constituting each column divided into the first part is determined differently depending upon the modulation method, wherein the number of rows constituting each column divided into the second part is determined depending upon the number of rows constituting each column divided into the first part.