To obtain a waste-treating device for efficiently burning liquid fuel.

In a waste-treating device 1 for treating the amount of decrease by heating waste according to the amount of heat obtained by burning while jetting liquid fuel in a spray using burners 8 and 14, pressure for jetting the liquid fuel can be switched to high and low levels. As a result, when the pressure is increased, the liquid fuel is formed into a fine particle shape to increase the contact area with air, thus obtaining a sufficient amount of air when burning the liquid fuel and hence preventing incomplete combustion from occurring and facilitating combustion, preventing a bad smell from occurring, at the same time withdrawing a large amount of heat from the liquid fuel. Also, when the pressure is decreased, the jetting amount of the liquid fuel per unit time decreases, thus saving the liquid fuel.