In the operation of smoking/burning type volume reduction treatment apparatus (1), referring to view (A), charcoal carbonized layer (T.sub.2) is spread over powdery ceramic layer (T.sub.1) in the state of having negative ion air fed through air supply inlet (H). Further, sawdust layer (T.sub.3) is spread thereover, and thereafter treatment subject layer (V) is piled thereon. In a temporary burning region of the carbonized layer (T.sub.2), the powdery ceramic layer (T.sub.1) exerts not only heat storing action but also heat radiation action. Referring to view (B), the interior of the sawdust layer (T.sub.3) is altered into temporary carbonized layer (T.sub.3 1) and temporary dried layer (T.sub.3 2). As the temporary burning region slowly moves upward, an under side of the treatment subject layer (V) is altered into dried layer (V.sub.1) and further, carbonized layer (V.sub.2) shown in view (C) is formed. Thereafter, this carbonized layer (V.sub.2) catches fire, so that burning region (V.sub.3) is formed in layered form in the treatment subject layer (V). Thus, smoking/burning starts. Accordingly, there can be provided a method wherein a burning region is securely formed in the treatment subject within the apparatus (1).