An apparatus for generating orthogonal sequences is disclosed which includes an M-sequence generator for providing a signal of M-sequence of which the component takes 0 or 1 and the period is N, and substitution means connected to the output of the M-sequence generator for substituting the component of the M-sequence. The substitution means substitute the component with A.sub.0 e.sup.j.phi..sbsp.0 when the value of the component is 0 and with A.sub.1 e.sup.j.phi..sbsp.1 when it is 1, where each of A.sub.0 and A.sub.1 is a positive real number, and the substitution is performed so that a trigonometric function f.sub.1 (.phi..sub.1 -.phi..sub.0) having a phase of (.phi..sub.1 -.phi..sub.0) is a ratio of two functions f.sub.2 (A.sub.1 /A.sub.0) which is a quadratic function of A.sub.1 /A.sub.0 with a coefficient of a linear function of N and f.sub.3 (A.sub.1 /A.sub.0) which is a linear function of A.sub.1 /A.sub.0 with a coefficient of a linear function of N, whereby the orthogonal sequence is generated from the substitution means.