In general, the active noise control technique has been adopted to reduce low frquency stationary noise. However, the conventional active noise control has mostly based on the physical quantities without consideration of human noise perception, such as acoustic potential energy, sound intensity, and sound power. From the standpoint of human noise perception, one might ask a question; How can we achieve the noise reduction which can be appreciated?" To find an appropriate answer of the question, loudness which is one of the most important subjective quantities in hearing sensation, is suggested as a cost function of active noise control. Firstly, a calculation procedure of loudness is studied to handle the loudness as a control cost function. Based on the procedure, the optimal condition of a control source which should be drived to reduce loudness at a control position, is derived. As a result, The control source condition of loudness control is exactly the same as one of acoustic potential energy control. It is, therefore, concluded that the conventional active noise control based on acoustic potential energy is reasonable in the sense of perceived loudness reduction.