A sunshade device configured to shield a window, comprising: a windup device; a screen attached to said windup device so as to be drawn therefrom and housed therein; a stay attached to a drawing-side edge of said screen and including a main body and a pair of connecting end portions at both end portions of said main body; and a pair of arms each arm including a distal end portion connected to the respective connecting end portion of said pair of connecting end portions of said stay so as to rotate relative thereto and a proximal end portion supported by said windup device so as to rotate relative thereto about a rotation shaft, said pair of arms being configured to change a position between a folded position in which said screen is housed and an extended position in which said screen is drawn through the rotary movement about said rotation shaft, each arm of said pair of arms including a pivot base including a one-end-side portion extending toward a side of a vertical frame of said window from said rotation shaft in said extended position and an other-end-side portion extending along the vertical frame of said window in a manner of being bent from a distal end portion of said one-end-side portion; and an arm portion connected to a distal end portion of said other-end-side portion of said pivot base so as to rotate relative thereto; characterized in that said pair of connecting end portions is attached to the both end portions of said main body; wherein each of the arm portions extends along the vertical frame of said window in said extended position; wherein each connecting end portion of said pair of connecting end portions of said stay includes a fixed portion fixed to the respective end portion of said main body; and an advancing/retracting portion to which said arm portion is connected so as to rotate relative thereto, said advancing/retracting portion being configured to move relatively close to or apart from said fixed portion along the drawing/housing direction of said screen; wherein said fixed portion and said advancing/retracting portion are biased in a direction of becoming apart from each other by a biasing member. a windup device; a screen attached to said windup device so as to be drawn therefrom and housed therein; a stay attached to a drawing-side edge of said screen and including a main body and a pair of connecting end portions at both end portions of said main body; and a pair of arms each arm including a distal end portion connected to the respective connecting end portion of said pair of connecting end portions of said stay so as to rotate relative thereto and a proximal end portion supported by said windup device so as to rotate relative thereto about a rotation shaft, said pair of arms being configured to change a position between a folded position in which said screen is housed and an extended position in which said screen is drawn through the rotary movement about said rotation shaft, each arm of said pair of arms including a pivot base including a one-end-side portion extending toward a side of a vertical frame of said window from said rotation shaft in said extended position and an other-end-side portion extending along the vertical frame of said window in a manner of being bent from a distal end portion of said one-end-side portion; and an arm portion connected to a distal end portion of said other-end-side portion of said pivot base so as to rotate relative thereto; characterized in that said pair of connecting end portions is attached to the both end portions of said main body; wherein each of the arm portions extends along the vertical frame of said window in said extended position; a pivot base including a one-end-side portion extending toward a side of a vertical frame of said window from said rotation shaft in said extended position and an other-end-side portion extending along the vertical frame of said window in a manner of being bent from a distal end portion of said one-end-side portion; and an arm portion connected to a distal end portion of said other-end-side portion of said pivot base so as to rotate relative thereto; characterized in that said pair of connecting end portions is attached to the both end portions of said main body; wherein each of the arm portions extends along the vertical frame of said window in said extended position; wherein each connecting end portion of said pair of connecting end portions of said stay includes a fixed portion fixed to the respective end portion of said main body; and an advancing/retracting portion to which said arm portion is connected so as to rotate relative thereto, said advancing/retracting portion being configured to move relatively close to or apart from said fixed portion along the drawing/housing direction of said screen; wherein a fixed portion fixed to the respective end portion of said main body; and an advancing/retracting portion to which said arm portion is connected so as to rotate relative thereto, said advancing/retracting portion being configured to move relatively close to or apart from said fixed portion along the drawing/housing direction of said screen; wherein said fixed portion and said advancing/retracting portion are biased in a direction of becoming apart from each other by a biasing member.