A window blind apparatus 1 includes a frame body 3 disposed in an opening portion 2; a plurality of slats 4 for opening and closing the opening portion 2; a link mechanism 5 for mutually connecting the slats 4; a raising and lowering mechanism 9 for raising and lowering the plurality of slats 4 in opening and closing the opening portion 2, by raising the slats 4, starting with a lowermost slat 8, and by lowering the slats 4, starting with the lowermost slat 8; and a reaction force generating mechanism 10 for imparting to the raising and lowering mechanism 9 a reaction force which is oriented in a direction opposite to the direction of the load of the slats 4 in the opening portion 2 and which increases or decreases in correspondence with an increase or decrease of the load of the slats 4 in the opening portion 2 corresponding to the number of the slats 4 being raised or lowered by the raising and lowering mechanism 9 in the opening portion 2.