A sunshade device configured to shield a window, comprising: a pair of rails disposed so as to have a gradually decreasing spacing therebetween at least at a part from a proximal end toward a distal end thereof; a windup device disposed between proximal ends of said pair of rails and including a windup shaft supported so as to rotate about an axis; a shade including a short side edge and a long side edge opposed to each other and configured to be drawn from and housed in said windup device, said long side edge being attached to said windup shaft; a stay attached to the short side edge of said shade; a pair of shafts respectively inserted into both ends of said stay so as to move along a longitudinal direction thereof, said pair of shafts being adapted to support the stay so as to rotate; a pair of runners respectively provided so as to move along said pair of rails and coupled to said pair of shafts; characterized by a rotation mechanism provided at least on one end side of said stay and causing said stay to change a position thereof upon reception of a force by which said shafts move along the longitudinal direction of said stay due to a change of the spacing between said pair of rails as said pair of runners moves along said pair of rails, wherein said rotation mechanism includes a protrusion provided to one of an inner peripheral portion of said stay and an outer peripheral portion of said shaft, and includes a guide recess provided to the other of the inner peripheral portion of said stay and the outer peripheral portion of said shaft, said rotation mechanism being adapted to cause, upon said shaft moving within said stay along the longitudinal direction thereof due to a change of the spacing between said pair of rails, said stay to change the position thereof through sliding contact of said protrusion with said guide recess, wherein said stay is provided with a cover body for covering gaps between window peripheral members located on a distal end side of said pair of rails and said stay in a state in which said shade is drawn, and wherein said rotation mechanism is adapted to cause said stay to change the position thereof such that said cover body covers the gaps between said window peripheral members and said stay in the state in which said shade is drawn. a pair of rails disposed so as to have a gradually decreasing spacing therebetween at least at a part from a proximal end toward a distal end thereof; a windup device disposed between proximal ends of said pair of rails and including a windup shaft supported so as to rotate about an axis; a shade including a short side edge and a long side edge opposed to each other and configured to be drawn from and housed in said windup device, said long side edge being attached to said windup shaft; a stay attached to the short side edge of said shade; a pair of shafts respectively inserted into both ends of said stay so as to move along a longitudinal direction thereof, said pair of shafts being adapted to support the stay so as to rotate; a pair of runners respectively provided so as to move along said pair of rails and coupled to said pair of shafts; characterized by a rotation mechanism provided at least on one end side of said stay and causing said stay to change a position thereof upon reception of a force by which said shafts move along the longitudinal direction of said stay due to a change of the spacing between said pair of rails as said pair of runners moves along said pair of rails, wherein said rotation mechanism includes a protrusion provided to one of an inner peripheral portion of said stay and an outer peripheral portion of said shaft, and includes a guide recess provided to the other of the inner peripheral portion of said stay and the outer peripheral portion of said shaft, said rotation mechanism being adapted to cause, upon said shaft moving within said stay along the longitudinal direction thereof due to a change of the spacing between said pair of rails, said stay to change the position thereof through sliding contact of said protrusion with said guide recess, wherein said stay is provided with a cover body for covering gaps between window peripheral members located on a distal end side of said pair of rails and said stay in a state in which said shade is drawn, and wherein said rotation mechanism is adapted to cause said stay to change the position thereof such that said cover body covers the gaps between said window peripheral members and said stay in the state in which said shade is drawn.