A fastener used for mounting a mounting object having an insertion rib onto a support body having a mounting aperture. The fastener is previously fitted to the insertion rib of the mounting object and then inserted into the mounting aperture of the support body by pressing the insertion rib thereinto, thereby removably mounting the mounting object on the support body. The fastener includes a fastener body having a shoulder portion. The shoulder portion is adapted to elastically engage an inner edge of the mounting aperture of the support body when the fastener is inserted into the mounting aperture with the insertion rib. The fastener further includes a gripper portion provided on the fastener body and having at least one gripper surface and at least one engagement projection formed thereon. The gripper surface is adapted to contact the insertion rib of the mounting object when the fastener is fitted to the insertion rib. The engagement projection is adapted to engage a slot formed in the insertion rib of the mounting object when the fastener is fitted to the insertion rib.