In the case of existence of second-hand market, some methods for economic depreciation measurement have been developed. Among them, we consider two method. Those are Box -Cox model by Halten and Wykoff and Ratio method of T-factor by Iowa State University. Here, we suggest a new measurement method of economic depreciation based on the above two methods. According to the new method, we can get the failure rate of a equipment under the appropriate assumption. Then we can measure the economic depreciation more simply.