Kira and Shidei (1967) and Odum (1969) mentioned that old-growth forests had low net primary production (NPP) and their total biomass reached to the steady state. From their views, old-growth forest were thought to be carbon neutrality. Recently, these forests are considered as a significant carbon sink and have high NPP. As a result of this controversy between the two hypotheses that gives the different feature of old-growth forests, an aim of this work is to study net ecosystem production (NEP) of the old-growth beech-oak forest on the eastern slope of Mt. Hakusan during 2012 to 2015 using the biometric based NEP measurement. This forest showed high NPP (6.14 ton C ha^-1 year^-1) which was similar to those of Takayama temperate deciduous forest. However, this forest had low soil respiration (R_s; 3.3 ton C ha^-1 year^-1) and low heterotrophic respiration (R_SOM; 2.17 ton C ha^-1 year^-1). The coarse woody debris respiration (R_CWD) was 1.60 ton C ha^-1 year^-1. Therefore, NEP (NEP = NPP-R_SOM-R_CWD) was 2.36 ton C ha^-1 year^-1. It was considered that this forest showed high NPP and positive value of NEP.