A structured illumination microscope , comprising: a polarization separation element having an inclined polarization separation film ; a brancher that is configured to include a first substrate on which a plurality of pixel electrodes are provided, a second substrate opposed to the first substrate , and a ferroelectric liquid crystal disposed between the first substrate and the second substrate , and branches polarized light through the polarization separation element from a light source into a plurality of diffracted light beams; an illumination optical system that is configured to illuminate a sample (X) with interference fringes formed by at least some of the diffracted light beams; an imaging optical system that is configured to form an image of the sample (X) irradiated with the interference fringes; an imaging device that is configured to take the image formed by the imaging optical system ; a demodulator that is configured to perform demodulation processing by using a plurality of the images taken by the imaging device ; and a controller that is configured to control a direction and a phase of the interference fringes, characterized in that the controller is configured to apply a first voltage pattern (VPa, VPc, VPe) to at least some of the pixel electrodes in a period for a first frame during which the imaging device takes the image of the sample (X), and apply a second voltage pattern (VPb, VPd, VPf) obtained by inverting the first voltage pattern (VPa, VPc, VPe) in a period for a second frame during which the imaging device takes the image of the sample (X), and the demodulator is configured to perform the demodulation processing by using at least an image taken in the first frame period and an image taken in the second frame period. a polarization separation element having an inclined polarization separation film ; a brancher that is configured to include a first substrate on which a plurality of pixel electrodes are provided, a second substrate opposed to the first substrate , and a ferroelectric liquid crystal disposed between the first substrate and the second substrate , and branches polarized light through the polarization separation element from a light source into a plurality of diffracted light beams; an illumination optical system that is configured to illuminate a sample (X) with interference fringes formed by at least some of the diffracted light beams; an imaging optical system that is configured to form an image of the sample (X) irradiated with the interference fringes; an imaging device that is configured to take the image formed by the imaging optical system ; a demodulator that is configured to perform demodulation processing by using a plurality of the images taken by the imaging device ; and a controller that is configured to control a direction and a phase of the interference fringes, characterized in that the controller is configured to apply a first voltage pattern (VPa, VPc, VPe) to at least some of the pixel electrodes in a period for a first frame during which the imaging device takes the image of the sample (X), and apply a second voltage pattern (VPb, VPd, VPf) obtained by inverting the first voltage pattern (VPa, VPc, VPe) in a period for a second frame during which the imaging device takes the image of the sample (X), and the demodulator is configured to perform the demodulation processing by using at least an image taken in the first frame period and an image taken in the second frame period. <EOS>