PURPOSE: To provide an illuminator for photographing for cinema and its method which varies the intensity of light.

CONSTITUTION: Light emitted from a light source passes through an opening part 36a and a part of a movable neutral density filter 50 next. The filter 50 is specially designed so as to provide variable density continuously increasing from one side part to the other side part. The intensity of light emitted by the illuminator is varied by varying the position of the filter 50, namely installing a high density part or a low density part at an optical path. A neutral density filter is selected to be nearly neutral in color and the color quality of light passing through there does not vary. In order to secure the perfect shielding of light, a light shielding plate 80 of opaque material selectively inserted to the optical path is provided.