A subject observation apparatus comprising: a light-emitting section configured for emitting a light to a subject; a spectral characteristic switching section configured to be operated to switch the light emitted from the light-emitting section between light having a first spectral distribution and light having a second spectral distribution that is different from the first spectral distribution; an image pickup section configured for detecting a scattering angle of a return light from the subject and configured for performing optical modulation on the return light in accordance with the scattering angle; said image pickup section comprising an optical system, an optical modulator and a signal output section configured for generating a signal to show a state of light scattering in the subject (102 A) based on the light subjected to the optical modulation by the optical modulator, and configured for outputting the generated signal; characterized in that the optical system is configured to emit an incident return light as a parallel light having an angle corresponding to an incident angle at which the return light enters the optical system, and the optical modulator comprises: a light-selective transmitting portion (1003b1); and a light-transmitting portion (1003b2), the optical modulator being configured such that, when a forward-scattering direction of the return light is set to zero degrees, return light having an incident angle with respect to the optical system that is equal to or larger than zero degrees and equal to or smaller than a predetermined angle passes through the light-transmitting portion (1003b2) and the light-transmitting portion (1003b2) is configured to transmit light having substantially all wavelengths; and return light having an incident angle with respect to the optical system that is equal to or larger than the a predetermined angle and smaller than 90 degrees is incident on the light-selective transmitting portion (1003b1) and the light-selective transmitting portion (1003b1) is configured to transmit light in wavelength bands corresponding to the first spectral distribution, and to shield light in wavelength bands other than wavelength bands corresponding to the first spectral distribution. a light-emitting section configured for emitting a light to a subject; a spectral characteristic switching section configured to be operated to switch the light emitted from the light-emitting section between light having a first spectral distribution and light having a second spectral distribution that is different from the first spectral distribution; an image pickup section configured for detecting a scattering angle of a return light from the subject and configured for performing optical modulation on the return light in accordance with the scattering angle; said image pickup section comprising an optical system, an optical modulator and a signal output section configured for generating a signal to show a state of light scattering in the subject (102 A) based on the light subjected to the optical modulation by the optical modulator, and configured for outputting the generated signal; characterized in that the optical system is configured to emit an incident return light as a parallel light having an angle corresponding to an incident angle at which the return light enters the optical system, and the optical modulator comprises: a light-selective transmitting portion (1003b1); and a light-transmitting portion (1003b2), the optical modulator being configured such that, when a forward-scattering direction of the return light is set to zero degrees, return light having an incident angle with respect to the optical system that is equal to or larger than zero degrees and equal to or smaller than a predetermined angle passes through the light-transmitting portion (1003b2) and the light-transmitting portion (1003b2) is configured to transmit light having substantially all wavelengths; and return light having an incident angle with respect to the optical system that is equal to or larger than the a predetermined angle and smaller than 90 degrees is incident on the light-selective transmitting portion (1003b1) and the light-selective transmitting portion (1003b1) is configured to transmit light in wavelength bands corresponding to the first spectral distribution, and to shield light in wavelength bands other than wavelength bands corresponding to the first spectral distribution.