A window shade device (50, 250) for vehicles that covers a window (12, 212) of a vehicle to be shielded and opened, comprising: a window shade (52, 252) configured to shield said window (12, 212); a windup device (56, 256) winding up said window shade (52, 252) to be drawn therefrom and housed therein; a guide and support mechanism (62, 262) that includes a guide path member (66, 266) including a guide path (66P, 266P) along a drawing and housing direction of said window shade (52, 252) and supports a movable member (64, 264) along the guide path (66P, 266P); and an arm (70, 270, 370) that includes one end serving as a shade coupling part (71, 271) coupled to a drawing-direction edge portion of said window shade (52, 252) and the other end rotatably supported by said movable member (64, 264) and is configured to change a posture thereof between a first posture in which said shade coupling part (71, 271) is located on the housing direction side of said window shade (52, 252) and a second posture in which said shade coupling part is located on the drawing direction side of said window shade (52, 252), characterized in that a first gear (72, 274, 374) is provided to said arm (70, 270, 370) and a second gear (78, 178, 278) is provided to at least a part of said guide path (66P, 266P), and the window shade device for vehicles further comprises a deceleration gear mechanism (80, 280, 380) that is provided so as to mesh with each of said first gear (72, 274, 374) and said second gear (78, 178, 278), and decelerates and transfers, upon meshing with said first gear (72, 274, 374), a rotational movement by meshing with said second gear (78, 178, 278) as a rotational movement for causing said arm (70, 270, 370) to change the posture thereof between said first posture and said second posture. a window shade (52, 252) configured to shield said window (12, 212); a windup device (56, 256) winding up said window shade (52, 252) to be drawn therefrom and housed therein; a guide and support mechanism (62, 262) that includes a guide path member (66, 266) including a guide path (66P, 266P) along a drawing and housing direction of said window shade (52, 252) and supports a movable member (64, 264) along the guide path (66P, 266P); and an arm (70, 270, 370) that includes one end serving as a shade coupling part (71, 271) coupled to a drawing-direction edge portion of said window shade (52, 252) and the other end rotatably supported by said movable member (64, 264) and is configured to change a posture thereof between a first posture in which said shade coupling part (71, 271) is located on the housing direction side of said window shade (52, 252) and a second posture in which said shade coupling part is located on the drawing direction side of said window shade (52, 252), characterized in that a first gear (72, 274, 374) is provided to said arm (70, 270, 370) and a second gear (78, 178, 278) is provided to at least a part of said guide path (66P, 266P), and the window shade device for vehicles further comprises a deceleration gear mechanism (80, 280, 380) that is provided so as to mesh with each of said first gear (72, 274, 374) and said second gear (78, 178, 278), and decelerates and transfers, upon meshing with said first gear (72, 274, 374), a rotational movement by meshing with said second gear (78, 178, 278) as a rotational movement for causing said arm (70, 270, 370) to change the posture thereof between said first posture and said second posture.