To provide an operation control device for a rotary kiln automatically operated under a favorable temperature for a long period irrelevant to treatment objects to be introduced and stably providing uniform and high-quality molten slag.

This operation control device dispenses with the installation of a temperature detector hardly bearing a high-temperature and sever environment, dispenses with an art of determining the temperature from the brightness and color tone of the molten slag to be hardly precisely grasped in the same environment, allows a treatment means 15 to grasp information on the molten slag temperature according to the treatment object material from the molten slag from a molten slag flowing-down position acquired by an image pickup apparatus 14 based on a relation between (the molten slag flowing-down position)-(information related to the molten slag temperature) preset according to the treatment object, and controls the heating by a heating device 7 based thereon.