Quantitative economic valuation has already been implemented for agriculture and forest by applying the substitution method. The external economic impact of agriculture and forest has been grasped by summing up each impact in previous literature. In some foreign countries including EU where dry field farming is centralized in agriculture, however, significance of environmental impact of agriculture and forest has widely been recognized. Thus this article attempts to present a new economic valuation method for the functions of agriculture and forest including their effects on the environment. The concept of System for Integrated Environmental and Economic Accounting (SEEA) is employed to indicate the value of agriculture and forest in the framework of national economy. Mäler's approach is applied to theoretically derive a SEEA with agriculture and forest, and then those in Japan are valuated in a SEEA context by referring to research materials of the Ministry of Agriculture, Forestry, and Fisheries of Japan.