In manufacturing, both productivity and energy-saving have been required for sustainable economic progress. This article proposes an operational condition estimation method for improving energy efficiency by monitoring energy consumption in production machines. Our proposed estimation method aims to analyze causalities among the productivity performance indices of QCDES and the factors of 4M + 2E for improving manufacturing process. They stand for Quality, Cost, Delivery, Ecology, Safety, Man, Machine, Material, Method, Environment, and Energy. In our proposed method, operational condition such as stop, idling, and tact delay, is estimated from the machine behavior that is extracted by the energy consumption, and the energy loss is quantified by the operational condition. Machine behavior can be extracted by energy consumption if the energy consumption is measured with short sampling time less than 1.0 second. According to the estimation results of the operational condition on our factory line, it was successfully to improve an operating rate and energy efficiency by recognizing energy loss, which means energy consumption of non-contributive to the productivity. The production volume was increased and energy consumption was reduced concurrently because the operators could easy to select improvement plans, because the energy loss is sorted to a cause.