To maintain a layer thickness of a refuse constant by providing a mounting means for freely moving a movable fire grate of a downstream side from an upstream side to a moving element to reduce its stroked between the reciprocating grate and moving element.

A mounting means 5 for freely moving a movable fire grate 3 of a downstream side from an upstream side to a moving element 4 by a moving margin S to reduce its stroke L is provided between the grate 3 and the element 4 of a longitudinal direction. According to this constitution, when the element 4 is reciprocated at a predetermined stroke L in the longitudinal direction, the grate 3 is reciprocated longitudinally to each fixed fire grate 2. In this case, the grate 3 of a lowermost site is freely moved that much corresponding to the moving margin S to the element to reduce its stroke. Accordingly, even if the stroke L and speed of the element 4 are constant, a refuse feeding time of the downstream side from the upstream side is shortened to tend to stay, and a refuse layer thickness can be maintained constant, thereby lengthening a residence time.