A guard bar has an inverse-U shape, and its inward end portion is configured to pass through a cross bar and be welded to the cross bar and its outward end portion is fixed to the cross bar via a junction member. The junction member has a reinforcement portion which is fastened together with a link bracket and the cross bar. Thus, there can be provided a seatback bar structure of a vehicle which can properly attach the guard bar, considering the manufacturing accuracy of extrusion molding of aluminum or aluminum alloy, and also can properly transmit a load inputted to the guard bar in a vehicle's rollover to a leg portion and side panels so as to achieve appropriate load dispersion.