PURPOSE: To more accurately indicate a storage level by automatically compensating a capacitance type level indicator even if the level indicator is influenced by the atmospheric variation of the inside of an aggregate storage bin.

CONSTITUTION: A storage level-indicating value is operated by adding a correction factor R to an output value from a level sensor 10 mounted on each section of an aggregate storage bin 4 and is indicated on an indication part 16. The correction factor R is preset as a constant before the operation of a plant is started. However, during a time zone wherein an operation of discharging aggregates from the aggregate storage bin 4 is stopped and an operation of throwing aggregates into the aggregate storage bin 4 is stopped, i.e., while the operation of the plant is being discontinued, if the output value from the level sensor 10 is varied, the correction factor R is corrected responding to the rate of its variation and the storage level-indicating value is prevented from changing. After that, the storage level-indicating value is operated using a correction factor Rx corrected.