<p>A rear frame (R) extending rearward and upward from a down frame (A) is constituted by joining a rear frame front half portion (B) and a rear frame rear half portion (C) left and right rear frame front half portions (B) are connected by a cross frame (49); and the rear frame rear half portion (C) extends further forward from its joint with the rear frame front half portion (B) and is joined to the cross frame (49). The cross frame (49A) supports a seat (16) through a storage box (34).</p>
