Disclosed is a sunshade device provided with a winding device; a screen which is installed in such a way as to be capable of being pulled out of, and placed in, the winding device; a stay which is installed on the pull-out end of the screen; and a pair of arms wherein the top ends thereof are connected to the stay in such a way as to be relatively rotatable, wherein the base ends thereof are supported in such a way as to be relatively rotatable about the rotational axis with respect to the winding device, and wherein by means of rotational movements about the rotational axis, it is possible to change positions between the folded position and the unfolded position. The aforementioned pair of arms are configured in such a way that in the unfolded position, one end portion of the rotational movement base section extends from the rotational axis toward the vertical frame portion of the window, that in this position, the arm section and the other end portion of the rotational movement base section extend along the vertical frame in such a way as to flex from the tip section of the one end portion of the rotational movement base section, and that in this position, the arm section and the rotational movement base section are connected in such a way as to be relatively rotatable.