A structured illumination apparatus includes a light modulator being disposed in an exit flux of light from a light source and in which a sonic wave propagation path is arranged in a direction traversing the exit flux of light; a driving unit generating a sonic standing wave in the sonic wave propagation path by giving a driving signal for vibrating a medium of the sonic wave propagation path to the light modulator; and an illuminating optical system making mutually different diffracted components of the exit flux of light passed through the sonic wave propagation path to be interfered with each other, and forming interference fringes of the diffracted components on an observational object.