PURPOSE: To facilitate positioning and to prevent entrance of discharge air to the rear of an air conditioner by a method wherein a plateform member is disposed between an air conditioner and a wall, a resilient substance is secured to the plateform member, and small holes for setting the mounting position of a mounting metal and holes for inserting the mounting metal are formed.

CONSTITUTION: Small holes 3 for marking the mounting position of a screw for mounting an air conditioner 17 are formed in the end parts on both sides of a plateform member 2 being the base plate for a mounting plate 1 between an air conditioner 17 and a wall 15, and holes 4 into which a screw 21 for mounting is insertable are formed in the end part on both sides. A resilient substance 5 is secured across the both sides to the plateform member 2. Thereby, a position where the screw 21 for mounting is mounted to the wall 15 is located accurately by marking the small hole 3, and the screw 21 can be inserted into the holes 4 to mount the screw. The air conditioner 17 is easily mounted in a position on the wall 15 through the resilient substance 5 and the mounting plate 1. Contaminated exhaust gas through an upper discharge port 19 is prevented from entering a gap between the device and the wall 15 by the resilient substance 15 and the wall 15 may be kept clean.