The invention provides a window sunlight-shielding device that enables the shielded area of the window to be set so as to be minimized, allows ventilation of a space between a roll screen and the window, and has an inexpensive and simple structure. The window sunlight-shielding device for shielding a window in which the upper end section of a roll screen installed on the upper part of the window on the outdoor side of a building is fixed to a winding shaft urged by an urging means in the winding direction, the window sunlight-shielding device being characterized in that the lower end section of the roll screen is supported by a support shaft material, one end of each of a pair of arms is linked to both end parts of the support shaft material so that the arms are disposed in a plane perpendicular to the axial direction of the support shaft material, and the other end of each of the arms is fixed to both sides of the window on the outdoor side via a hinge structure enabling the arms to be held at a desired turning angle.