PURPOSE: To quickly perform dimming without controlling the light output of a light source by arranging a thermo-chromic film oppositely to the light source, and connecting a control means to a heating system heating the thermo- chromic film.

CONSTITUTION: A thermo-chromic film 6 is arranged oppositely to a light source 2, a control means 12 is connected to a heating system 9 heating the thermo- chromic film 6, the temperature of the thermo-chromic film 6 is changed via the drive control of the heating system 9 by the control means 12 to change permeability, thus the luminous quantity is adjusted. Dimming can be quickly performed without controlling the light output of the light source 2, and an illumination device having a practical dimming function can be obtained with a simple structure.