The present invention provides a treating unit of activated sludge for wastewater treatment and a treating apparatus having the same. The treating unit is constructed by a cage-shaped supporting structure which defines an interior space for containing the microbial cell therein. The present invention provides a measure for simultaneous removal of organics and nitrogen compounds from the wastewater under a condition of controlled aeration, and makes the configuration of treating apparatus as well as the treating process more simplified. It is also an alternative to replace the traditional A2O process. According to the present invention, the design of sludge return, which is essential for the conventional activated sludge treatment, is not needed. Moreover, the present invention is compatible with the conventional activated sludge treatment process and is advantageous in its short start-up period during which a stable operation is achievable.