To optionally adjust the heating time even when a rotary drum is short-sized by limiting a residing period of time in the rotary cylindrical body, and making a harmful object which is decomposed and deposited from an article to be treated by bringing the harmful object into contact with a chemical to make the harmful object react with the chemical.

When applied to a waste treating equipment, hot gas is generated by a hot gas generating means 12, and a rotary cylindrical body 2 is heated to a temperature in response to the heating purpose by the hot gas. Then, an article to be treated (e.g. waste), is mixed with a chemical. As the chemical, a substance which forms a non-toxious chloride by reacting with hydrogen chloride, e.g. sodium bicarbonate is thrown into the rotary cylindrical body 2, and a toxious component is deposited from the article to be treated by a thermal decomposition, and at the same time, the toxious component is made to react with the chemical. This decomposing treatment is treated at a temperature (200-350°C) and a period of time. The treating time is adjusted by normally and reversely controlling the rotary cylindrical body 2 by a rotation-driving means 5, and advancing and retracting the article to be treated. By the adjustment, the residing time can be kept long, and the dimension in the longitudinal direction of the rotary cylindrical body can be shortened.