To compost excrement with sawdust by putting sawdust, etc., as a medium into a closed waste tank equipped with an agitator means to convert the excrement to heat energy by fermentation of aerobic microorganism and splashing this.

A matter 8 containing a lot of dried organic carbon (sawdust, etc., called a C/N balancer) is housed from the feeding and take-out port 5 of a fermentation tank (waste tank) 1 of sealed structure to be heated to about 20° C by a heating means 4. At the time of movement at a toilet stool 7 in this state, the C/N balancer absorbs excrement including a lot of water and nitrogen. By driving the agitator mixing means 2 for 1 to 2 sec every other 6 to 8 hours by a driving part 3 at this time, excrement 8 is mixed with the C/N balancer to be fermented by the aerobic microorganism. As an internal temperature rises to 50 to 70°C, colibacillus, the eggs of parasite, etc., are killed to obtain a sanitary compost.