The invention relates to a folding stroller such as a buggy having a seat. The frame of the stroller includes a pull/push rod; right and left front wheel rods, each provided with a front wheel; and a cross bar system provided between the front wheel rods. When the stroller is unfolded, the cross bar system fixes the distance between the wheel-carrying ends of the front wheel rods. The cross bar system is constructed such that when the stroller is folded, the distance between the wheel-carrying ends of the front wheel rods is less than when the stroller is unfolded. The cross bar system includes a right part, a left part and a middle part, which are provided with an interlocking member which, on rotation of the middle part, pushes the left and right parts apart and mutually fixes them.