PURPOSE: To dim illumination so as to reduce illumination electric power by controlling the upward and downward movement and vane angle of a dimming member through the detection of direct light included in sunlight, and introducing the sunlight into a room in a comfortable view environment not dazzling a person in the room.

CONSTITUTION: A direct light detector 4 is composed of a photo diode array(PDA) 1 arranged vertically on a wall face 5 close to a window inside a transparent protection case 3, a shading plate A2 arranged vertically in the center of the length direction of the PDA 1, and a position determination part determining position relation between the position of the sun and the window depending on date and time. The existence of direct light towards the window of sunlight is detected based on the level changes of the signals according to addresses of the PDA 1 by means of the shading plate A2 and the output signal from the position determination part, and the upward and downward movement and vane angle of a dimming member are controlled thereby.