A transmission method for transmitting digital data, comprising: encoding a block of data of a predetermined length with an error correction code; generating a real-valued symbol sequence including N s real-valued symbols by mapping the encoded block of data onto real-valued symbols a predetermined number of bits at a time; converting D-dimensional vectors into D-dimensional rotated vectors by multiplying each of the D-dimensional vectors by a D x D orthogonal matrix, each of the D-dimensional vectors having D of the real-valued symbols in the real-valued symbol sequence as elements, each of the D-dimensional rotated vectors having D real symbols as elements; and generating a complex symbol sequence from N s real symbols resulting from the conversion, the complex symbol sequence including N c = N s /2 complex symbols, wherein the complex symbol sequence is generated by: mapping the D real symbols of each D-dimensional rotated vector onto D/2 contiguous complex symbols, and thereby generating a first complex symbol sequence including N c first complex symbols from the N s real symbols resulting from the conversion; generating a second complex symbol sequence including the N c complex symbols by inserting a delay of D/2 symbols with a predetermined period between a real component and an imaginary component of each of the N c first complex symbols in the first complex symbol sequence; and performing processing equivalent to writing the N c complex symbols in the second complex symbol sequence column by column into an interleaver matrix having D rows, and to reading the N c complex symbols row by row from the interleaver matrix and transmitting the read sequence of Nc complex symbols. encoding a block of data of a predetermined length with an error correction code; generating a real-valued symbol sequence including N s real-valued symbols by mapping the encoded block of data onto real-valued symbols a predetermined number of bits at a time; converting D-dimensional vectors into D-dimensional rotated vectors by multiplying each of the D-dimensional vectors by a D x D orthogonal matrix, each of the D-dimensional vectors having D of the real-valued symbols in the real-valued symbol sequence as elements, each of the D-dimensional rotated vectors having D real symbols as elements; and generating a complex symbol sequence from N s real symbols resulting from the conversion, the complex symbol sequence including N c = N s /2 complex symbols, wherein the complex symbol sequence is generated by: mapping the D real symbols of each D-dimensional rotated vector onto D/2 contiguous complex symbols, and thereby generating a first complex symbol sequence including N c first complex symbols from the N s real symbols resulting from the conversion; generating a second complex symbol sequence including the N c complex symbols by inserting a delay of D/2 symbols with a predetermined period between a real component and an imaginary component of each of the N c first complex symbols in the first complex symbol sequence; and performing processing equivalent to writing the N c complex symbols in the second complex symbol sequence column by column into an interleaver matrix having D rows, and to reading the N c complex symbols row by row from the interleaver matrix and transmitting the read sequence of Nc complex symbols. mapping the D real symbols of each D-dimensional rotated vector onto D/2 contiguous complex symbols, and thereby generating a first complex symbol sequence including N c first complex symbols from the N s real symbols resulting from the conversion; generating a second complex symbol sequence including the N c complex symbols by inserting a delay of D/2 symbols with a predetermined period between a real component and an imaginary component of each of the N c first complex symbols in the first complex symbol sequence; and performing processing equivalent to writing the N c complex symbols in the second complex symbol sequence column by column into an interleaver matrix having D rows, and to reading the N c complex symbols row by row from the interleaver matrix and transmitting the read sequence of Nc complex symbols.