To provide a seal gap adjusting method in a rotary regenerating heat exchanger wherein it can contribute to continuous operation of a plant, and the whole apparatus is simplified to reduce the cost.

A gap value between a sector plate 2 and a high temperature side radial seal is previously measured for each load of the plant and is stored in a controller 5. A varying load signal is received upon operation, and an instruction signal is sent to a motor 4 so as to hold a stored gap value for the load. Thus, the sector plate 2 is displaced through a screw Jack 3.