To increase support strength by bypassing a horizontal part of a frame molded in an L shape on the upper end of a roll-over protective structure, and supporting a lower end part of frames by a support installed on the roll- over protective structure when supporting the frames of a sun visor for covering an upper part of a seat by a gate-shaped roll-over protective structure erected in the rear of the seat.

In an agricultural tractor 1, left/right lower end parts of a roll-over protective structure 32 molded in a gate shape are installed in a rear axle case. A nonvertical part 32a formed in an upper part of the roll-over protective structure 32 is fitted to left/right fitting bodies 33a of a support 33, and a lock pin 33c is inserted into and fixed to these lock holes 33b. Left/ right support frames 35 of a sun visor 34 for covering an upper part of a seat are inserted into left/right support cylinders 33e arranged in a support bar part 33d of the support 33, and a horizontal part of the frames 35 is positioned by abutting to the upper end of the roll-over protective structure 32. That is, support strength of the frames 35 and the sun visor 34 is increased by supporting the frames 35 and the roll-over protective structure 32 at two points of the support 33 and an upper end part of the roll-over protective structure 32.