To provide a heat treating system capable of stably thermally decomposing when resin waste and organic waste of high moisture contents are mixed and subjected to thermal decomposition, and to provide a dryer capable of effectively drying the organic waste of high moisture contents.

The heat treating system is provided with the dryer 30 drying the organic waste of high moisture contents 14 and a thermal decomposition apparatus 40 subjecting to thermal decomposition by housing the resin waste 12 and the organic waste of high moisture contents 14 dried in the dryer 30, and mixing and heating them. The dryer 30 possesses a front stage drying furnace 132 and a rear stage drying furnace 134 and the volume of housing the organic waste of high moisture contents 14 in the high moisture content 132 is larger than that of housing the organic waste of high moisture content 14 in the rear moisture content 134.