In order to stack two or more empty packaging boxes stably, a mechanism to spread and slack the corners of the multifunctional business telephones’ individual packaging boxes has been applied. After completing the installation work of the business phones, it is possible to store quickly the stacked empty boxes in the empty boxes of the main unit, to take them compactly and to discard them as they are. It shortens the working time from demolition of the empty boxes to the withdrawal at the site.