A vehicle-mounted apparatus installing unit (101) with switches (21a, 21b) protruding into the cabin is provided with: a cluster panel (10) facing the interior of the cabin; a front case (20) supporting the switches (21a, 21b) in such a manner as to protrude from the cluster panel (10); and a rear case (30) attached to the cluster panel (10) on the opposite side from the cabin and forming a space (30a) with the cluster panel (10) in which the front case (20) is included. The front case (20) is fixed onto the cluster panel (10) via engagement between a first engaging projection (23a) and a first engaging hole (13a). The engagement is released when a load pressing the switches (21a, 21b) toward the cluster panel (10) exceeds a predetermined load.