In April, 2009 the Japan's Methane Hydrate R&D Program moved on to Phase 2 in order to establish the technology platform for commercial gas production from offshore-Japan methane hydrates, and we are planning the world's first offshore methane-hydrate gas production test in FY 2012. Prior to the production test, we carried out preliminary evaluation on economics of depressurization-induced gas production from a hypothetical methane-hydrate filed in Eastern Nankai Trough. Our economic evaluation consists of the following steps. 1) Setting of a hypothetical field and production system by considering the condition of the Eastern Nankai Trough methane hydrates, such as water depth, distance from coast, hydrate-layer thickness and permeability. 2) Simulation of single-well production performance by using a numerical simulator. 3) Making well completion and field production schedules based on the simulated well performance. 4) Estimation of development costs. 5) Gas-price forecasting. 6) Discounted cash flow (DCF) analysis. We selected a production system of SPAR platform plus subsea well completions, and these costs were estimated by using the Oil and Gas Supply Module (OGSM) 2009 of EIA. The field development schedule (the number and timing of wells completed) was determined to keep a constant field gas production rate of about 2 million cubic meters per day as possible. As a result of economic evaluation, the field development project assuming 20-years gas production starting from 2019 was found to generate the net present value of about 95.5 billion yen with discount rate = 10 % (IRR = 41.7 %) under the most preferable conditions. About a half of the total development was spent by well drilling and completion. Although this study assumed a simplified and small field model, it showed the gas production from oceanic hydrates would be economically viable if our future research can remove risks und uncertainties in geological and engineering problems.