A sunshade device configured to shade a window surrounded by a window frame comprising vertical frames which have housing groove parts that are open toward the center in a width direction of a vehicle and are disposed on both sides of the width direction of the vehicle, comprising: a windup device; a screen mounted to said windup device so as to be drawn therefrom and housed therein; a stay mounted to a drawing-side edge of said screen; and a pair of arms each including a distal end portion connected to 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 axis, said pair of arms being configured to change a position between a folded position for causing said screen to be housed and an extended position for causing said screen to be drawn through a rotary movement about said rotation axis, and in said extended position, said pair of arms being configured to be housed in said housing groove parts, wherein: said pair of arms each include, in said extended position, an extending-toward-frame portion extending toward the vertical frame of said window from said rotation axis and an extending-along-frame portion extending along the vertical frame of said window in a manner of being bent from a distal end portion of said extending-toward-frame portion; said extending-along-frame portion includes a distal-end-side portion and a proximal-end-side portion integrally formed with said extending-toward-frame portion, said distal-end-side portion and said proximal-end-side portion being connected so as to rotate relative thereto, and said extending-along-frame portion is extendable and retractable along a longitudinal direction thereof and includes a biasing member biased in an extending direction. a windup device; a screen mounted to said windup device so as to be drawn therefrom and housed therein; a stay mounted to a drawing-side edge of said screen; and a pair of arms each including a distal end portion connected to 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 axis, said pair of arms being configured to change a position between a folded position for causing said screen to be housed and an extended position for causing said screen to be drawn through a rotary movement about said rotation axis, and in said extended position, said pair of arms being configured to be housed in said housing groove parts, wherein: said pair of arms each include, in said extended position, an extending-toward-frame portion extending toward the vertical frame of said window from said rotation axis and an extending-along-frame portion extending along the vertical frame of said window in a manner of being bent from a distal end portion of said extending-toward-frame portion; said extending-along-frame portion includes a distal-end-side portion and a proximal-end-side portion integrally formed with said extending-toward-frame portion, said distal-end-side portion and said proximal-end-side portion being connected so as to rotate relative thereto, and said extending-along-frame portion is extendable and retractable along a longitudinal direction thereof and includes a biasing member biased in an extending direction. said pair of arms each include, in said extended position, an extending-toward-frame portion extending toward the vertical frame of said window from said rotation axis and an extending-along-frame portion extending along the vertical frame of said window in a manner of being bent from a distal end portion of said extending-toward-frame portion; said extending-along-frame portion includes a distal-end-side portion and a proximal-end-side portion integrally formed with said extending-toward-frame portion, said distal-end-side portion and said proximal-end-side portion being connected so as to rotate relative thereto, and said extending-along-frame portion is extendable and retractable along a longitudinal direction thereof and includes a biasing member biased in an extending direction.