A plurality of main frame members that are commonly usable for a plurality of types of straddled vehicles are fabricated. Left and light pivot shaft supporting portions are provided in each main frame member. The left and right pivot shaft supporting portions include left and right hole formable portions in which left and right pivot holes are formable and which have areas larger than an area of a head portion of a pivot shaft, respectively. One of the pivot shaft supporting portions includes a rotation restricting portion that restricts rotation of the head portion of the pivot shaft inserted into the pivot hole. The pivot holes are respectively formed at predetermined positions at pivot shaft supporting portions of each main frame member, and the predetermined positions are different in accordance with a type of a vehicle for which each main frame member is to be used.