PURPOSE: To improve safety of a rubbish pit door for rubbish burning plant by constructing the door with upper and lower doors such that the lower door is interlocked with opening motion of the upper door to be folded onto the under face of the upper door thereby reducing projection into the pit when the door is opened.

CONSTITUTION: Upon depression of an open door button, a first hydraulic cylinder 15 functions to rotate an upper door 3 around a shaft 10 to the inside of a pit 1. Consequently, a lower door 4 lifts under freely suspendable state with respect to the upper door 3. When the upper door 3 lifts to an open position, an upper door upper limit (not shown in fig.) functions to lock the upper door 3 to the open position. At the same time, a second hydraulic cylinder 18 functions to lift the lower door 4 and fold the lower door 4 to the underface side of the upper door 3. A safety lamp 11 is also lighted. With such arrangement, projecting amount of door into the pit can be reduced when the door is opened, resulting in improved safety.