Agriculture and forestry produce various environmental benefits such as CO2 absorption and water storage as well as food and energy crops. Environmental benefits contribute to improving the environment. This means agriculture has the potential to improve the environment. By measuring such potential, we can understand agriculture's affect on the environment. However, both environmental loads and benefits should be taken into account because agriculture produces not only environmental benefits but also environmental loads, and both affect the agricultural potential for improving the environment. Furthermore, as potential cannot be calculated by a single environmental factor, it is necessary to consider various environmental factors in the measurements. Therefore, a new comprehensive indicator is required for understanding the potential to improve the environment. To develop the indicator, the National Accounting Matrix including Environmental Accounts (NAMEA) is applied to manage information concerning economies and environments, and the Ecological Footprint (EF) can also be adapted to integrate individual environmental factors. In this paper, a new indicator is introduced that measures the agricultural sector's potential for improving the environment. A trial estimation of the indicator is done by using a case study from Hokkaido, Japan.