As interest in sustainable and eco-friendly energy increases, demand for hydrogen energy is also increasing. Hydrogenogenic CO oxidation (CO + H2O→ CO2+H2) has the potential for H2 production as a clean renewable fuel. In this study, it was developed economic biological hydrogen technology utilizing renewable resources such as industrial by-product gas including carbon monoxide, using the Thermococcus Onnurineus NA1. Pilot plant was designed and constructed in order to convert from CO in LDG which is a by-product gas of steel mill to H2 and implemented the technology through demonstration. 2.4Nm3/h of LDG was continuously supplied to 1t culture medium reaction tank. As a result, 97% CO gas in LDG was converted into hydrogen gas and hydrogen content in the product gas is 40% or more. The purity of product gas was increased to 99.9% hydrogen gas by PSA. The high purity hydrogen gas was successively used to generate electricity by fuel cell system which has developed in Hyundai Steel. This results is the first demonstration of H2 production from steel mill by-product gas by a carboxydotrophic hydrogenogenic microbe.