An imaging system includes: an illumination unit configured to emit illumination light for illuminating a subject; a light receiving unit in which pixels are arranged two-dimensionally, each pixel being configured to receive light and generate an electric signal by performing photoelectric conversion of the light; a readout unit configured to sequentially read out the electric signal from the light receiving unit for every horizontal line; and an illumination controller configured to keep intensity of the illumination light emitted from the illumination unit constant in at least a part of a readout period where the readout unit reads out the horizontal line of the light receiving unit in one frame or one field period, and configured to variably control an illumination time of the illumination light emitted from the illumination unit, outside the readout period.