The present disclosure includes: a mid-plate configured to support a bottom side of a battery module from a bottom side of a vehicle body; a fastening member fastened through a space in which the mid-plate and the battery module are mounted and configured to fix the mid-plate to the vehicle body; a mounting pipe provided at a top side of the mid-plate and configured to support a pressure applied to the vehicle body from a bottom side of the mid-plate, wherein the fastening member passes through the mounting pipe; a mounting support configured to fix the mounting pipe to the mid-plate, wherein the fastening member passes through the mounting support; and a shield plate coupled to the bottom side of the mid-plate and configured to surround a bottom-side coupling portion of the mounting support while allowing the fastening member to pass therethrough.