To perform a stable aerobic treatment in a short time and to efficiently recover excess sludge with high density by combining integrally a floating separation part with an aerobic filter bed part.

The aerobic treatment is performed with a waste water treating device (hereinafter, called aerobic treating tank) 10 consisting of a floating treatment integrated aerobic filter bed having the floating separation part 11 arranged at the upper part and the aerobic filter bed part 12 arranged at the lower part. By arranging the floating separation part 11 above the aerobic filter bed part 12 and executing a non-chemical pressure floating treatment, the clogging of a contact material 21 of the aerobic filter bed part 12 is prevented since easy-floating components such as hair, oil portion, scum or the like is completely removed for a short time and the load of the aerobic filter bed part 12 is remarkably reduced since the removing ratio of suspended components is high compared to the usual precipitation. Then, the stable aerobic treatment is performed for a short time and the excess sludge is efficiently recover with high density.