To provide equipment for volume-reducing waste sludge efficiently.

The equipment for volume-reducing waste sludge is composed of: a sludge storage tank 10 in which waste sludge S is stored temporarily and which has an air diffuser 11 and a feed pump 12; an ozone mixing tank 70 to which the waste sludge S in the sludge storage tank 10 is supplied automatically by the feed pump 12 and which has a hyperfine air bubble unit 71 at the bottom thereof; a digestion decomposition unit 20 to which the waste sludge S in the ozone mixing tank 70 is supplied and which has therein a digestion decomposition tank 21 equipped with a filtration membrane group 22 and an air diffuser 23; an ozone generator 30 for supplying ozone to the hyperfine air bubble unit 71; a treated water storage tank 40 for temporarily storing the treated water W, which is contacted with the filtration membrane group 22 and made to pass through a sterilization unit 41 arranged inside the treated water storage tank, and then discharging the temporarily-stored treated water; and a waste ozone removal unit 50 for treating the waste ozone, which is not dissolved in the ozone mixing tank 70 and the digestion decomposition tank 21, to decrease the ozone concentration to a regulated value or less and discharging the treated waste ozone.