This electronic document is a 'live' template and already defines the components of your paper [title, text, heads, etc.] in its style sheet. Microgrid (MG) is becoming a key strategy to implement smart grid as time passes by. MG has been applied to various purposes such as local communities, buildings, factories, etc. HEMS stands for home energy management system and is the application for a home which is the basic unit of residential load. HEMS could be applied to aggregated loads as well as detached houses. An apartment can be a good example. It is composed of hundreds or thousands of individual homes. In this context, it is possible to model a load as an aggregated form of autonomous smaller units. The concept is extendable to other kinds of loads in that all kinds of loads have their sub-units. Therefore, HEMS is the basic building block for multi-Agent approach to demand side. Each HEMS is an independent and autonomous agent for the bigger society like an apartment at the upper level. At the same time, it has its subunits like home electronics and is required to manage all the components. HEMS is not only an agent for the bigger part of a load but also an multi-Agent system (MAS) by itself. This paper proposes an operation mechanism for HEMS in the context of MAS.