It is very important that sellers provide reasonable reserve prices for auction items in internet auction systems. Recently, an agent has been proposed to generate reserve prices automatically based on the case similarity of information retrieval theory. However, one of its drawbacks is that the recent trend of auction prices is not reflected in the generated reserve prices, because it suggests the bid price of the most similar item from the past auction data. In this paper, in order to overcome the problem, we propose a new method that generates reserve prices based on the moving average of time series analysis, in which more weight is provided to the recent bid prices. Through performance experiments, we show that the successful bid rate can be increased by preventing sellers from making unreasonable reserve prices.