A method for controlling a storage/retrieval device in a flat storage facility which includes a storage item placement plane and a storage/retrieval device, in which the storage/retrieval device includes: a Y-direction laterally moving member that is freely moved horizontally and laterally in a Y direction at a certain height above the storage item placement plane; a carriage that is freely moved horizontally in an X direction perpendicularly intersecting the Y direction on the Y-direction laterally moving member; and a storage item gripping means that is provided in the carriage so as to be freely raised and lowered, and in which the storage/retrieval device performs storage/retrieval operation on a storage item between the storage/retrieval device and respective storage item placement points (Cp) set on the storage item placement plane, wherein the storage item placement plane is divided into a plurality of unit sections, for each of the unit sections, a difference in height with respect to a reference plane of the storage item placement plane is measured and recorded, and when the storage/retrieval operation is performed with the storage/retrieval device, a lowering distance of the storage item gripping means with respect to the carriage is adjusted by the difference in height of the unit section to which the storage item placement point (Cp) of a storage/retrieval target belongs, characterized in that: the unit section set for a region where a degree of unevenness is high within the storage item placement plane is decreased in size, and the unit section set for a region where the degree of unevenness is low within the storage item placement plane is increased in size, and/or with respect to a specific unit section in which a difference in height that is equal to or more than a set value, the specific unit section is further divided into a plurality of small sections (a), for each of the small sections (a), the difference in height is measured, and when the storage/retrieval is performed on the storage item placement point t (Cp) belonging to the specific unit section, the lowering distance of the storage item gripping means with respect to the carriage is adjusted by the difference in height of the small section (a) to which the storage item placement point (Cp) of the storage/retrieval target belongs. the unit section set for a region where a degree of unevenness is high within the storage item placement plane is decreased in size, and the unit section set for a region where the degree of unevenness is low within the storage item placement plane is increased in size, and/or with respect to a specific unit section in which a difference in height that is equal to or more than a set value, the specific unit section is further divided into a plurality of small sections (a), for each of the small sections (a), the difference in height is measured, and when the storage/retrieval is performed on the storage item placement point t (Cp) belonging to the specific unit section, the lowering distance of the storage item gripping means with respect to the carriage is adjusted by the difference in height of the small section (a) to which the storage item placement point (Cp) of the storage/retrieval target belongs.