A phase difference observation apparatus , comprising: a light source ; an illumination optical system configured to guide illumination light from the light source to an observation target object in a cell culture vessel ; an imaging optical system configured to form an optical image of the observation target object on an image sensor ; a control unit , wherein the illumination optical system comprises a spatial modulator configured to change an intensity distribution of the illumination light, characterized in that : the control unit contains intensity distribution correction information associating a position of the imaging optical system with respect to the cell culture vessel with an intensity distribution of illumination light at the position of the imaging optical system, the control unit is configured to acquire imaging system position information, which is the position of the imaging optical system, and the control unit is configured to change an intensity distribution of illumination light in the spatial modulator on the basis of the imaging system position information and the intensity distribution correction information; and the phase difference observation apparatus further comprises: a first moving unit that can move the light source and the illumination optical system; and a second moving unit that can move the imaging optical system. a light source ; an illumination optical system configured to guide illumination light from the light source to an observation target object in a cell culture vessel ; an imaging optical system configured to form an optical image of the observation target object on an image sensor ; a control unit , wherein the illumination optical system comprises a spatial modulator configured to change an intensity distribution of the illumination light, characterized in that : the control unit contains intensity distribution correction information associating a position of the imaging optical system with respect to the cell culture vessel with an intensity distribution of illumination light at the position of the imaging optical system, the control unit is configured to acquire imaging system position information, which is the position of the imaging optical system, and the control unit is configured to change an intensity distribution of illumination light in the spatial modulator on the basis of the imaging system position information and the intensity distribution correction information; and the phase difference observation apparatus further comprises: a first moving unit that can move the light source and the illumination optical system; and a second moving unit that can move the imaging optical system. the control unit contains intensity distribution correction information associating a position of the imaging optical system with respect to the cell culture vessel with an intensity distribution of illumination light at the position of the imaging optical system, the control unit is configured to acquire imaging system position information, which is the position of the imaging optical system, and the control unit is configured to change an intensity distribution of illumination light in the spatial modulator on the basis of the imaging system position information and the intensity distribution correction information; and the phase difference observation apparatus further comprises: a first moving unit that can move the light source and the illumination optical system; and a second moving unit that can move the imaging optical system. a first moving unit that can move the light source and the illumination optical system; and a second moving unit that can move the imaging optical system. <EOS>