After the liberalization of electricity market in Japan, New entry electricity suppliers start to supply electricity to residential sectors. Because they don't have as many power generation resources as conventional electric companies, they need to know whether their customer's electricity demand pattern match with their generation resources characteristics for avoid procuring shortage electricity from electricity trade market. In addition, they need to estimate electricity demand accusatory in mid to long term for business planning. In this paper, as a basic study for estimation of aggregated households' electricity demand pattern characteristics, we survey 1,720 households about their family structure and monthly electricity usage in one or two years, and evaluate monthly electricity demand characteristics to classify seasonal electricity demand ratio pattern against annual average electricity demand. As a result, we classify 1,720 households in 15 groups and correlate the household ratio of each group and household's attributes such as house type and number of family members. Then, we propose a method to estimate the monthly electricity demand of aggregated households based on the ratio of each group.