A method of manufacturing a semiconductor optical element having an active layer containing quantum dots, in which density of the quantum dots in a resonator direction in a portion of the active layer in which density of photons is high, relative to the density of the quantum dots in a portion of the active layer in which the density of photons is relatively low, includes forming the quantum dots in the active layer so that the distribution density is uniform in a resonator direction; and diffusing or implanting an impurity non-uniformly in the resonator direction in the active layer in which quantum dots are uniformly distributed, thereby disordering some of the quantum dots and forming a non-uniform density distribution of the quantum dots in the resonator direction in the active layer.