A fastening apparatus for a purpose-built vehicle comprising an indoor space, comprising: a first fastener configured to be fixed to a first structure, the first structure being a top hat or a battery module of the vehicle; a second fastener coupled to a case configured to be fixed to a second structure, the second structure being a chassis frame of the vehicle, and configured to have the first fastener inserted therein; a fixing unit movably installed in the second fastener and configured to move in a direction that intersects a direction in which the first fastener is inserted, and to selectively limit relative movements of the first fastener and the second fastener; and an elevation unit installed in the case in a way to move up and down, and configured to be moved up and down by an external force that is applied from a work tool and adjust the direction in which the fixing unit moves, characterized in that the elevation unit comprises: an elevation member disposed to surround the second fastener and installed in a way to be slidable in a length direction of the second fastener; an elevation guide member extended in parallel to a length direction of the elevation member, and on which a rail part formed in the case is seated; and a guide member provided between the elevation member and the second fastener and configured to provide guidance to a movement of the fixing unit while operating in conjunction with an elevation movement of the elevation member. a first fastener configured to be fixed to a first structure, the first structure being a top hat or a battery module of the vehicle; a second fastener coupled to a case configured to be fixed to a second structure, the second structure being a chassis frame of the vehicle, and configured to have the first fastener inserted therein; a fixing unit movably installed in the second fastener and configured to move in a direction that intersects a direction in which the first fastener is inserted, and to selectively limit relative movements of the first fastener and the second fastener; and an elevation unit installed in the case in a way to move up and down, and configured to be moved up and down by an external force that is applied from a work tool and adjust the direction in which the fixing unit moves, characterized in that the elevation unit comprises: an elevation member disposed to surround the second fastener and installed in a way to be slidable in a length direction of the second fastener; an elevation guide member extended in parallel to a length direction of the elevation member, and on which a rail part formed in the case is seated; and a guide member provided between the elevation member and the second fastener and configured to provide guidance to a movement of the fixing unit while operating in conjunction with an elevation movement of the elevation member. an elevation member disposed to surround the second fastener and installed in a way to be slidable in a length direction of the second fastener; an elevation guide member extended in parallel to a length direction of the elevation member, and on which a rail part formed in the case is seated; and a guide member provided between the elevation member and the second fastener and configured to provide guidance to a movement of the fixing unit while operating in conjunction with an elevation movement of the elevation member.