Abstract: A library apparatus capable of being manufactured at low cost, in which a cartridge can be moved accurately without high mechanical precision. The library apparatus comprises a plurality of cells each for containing a cartridge, a reference cell unit, an accessor unit, a passage unit, at least a drum unit, at least a drive unit, a guide rail and an accessor. The accessor has a high-accuracy diagnostic cell. The error between the light axis of a photoelectric sensor of the accessor and the operation axis of a hand unit of the accessor is measured by inserting and withdrawing a high-accuracy diagnostic cartridge into and out of the diagnostic cell. Also, a position correction value and a sensor sensitivity correction value for the accessor actually moving to a cell are determined. On the basis of the error and correction values thus obtained, a table showing the relative positions of all the cells is prepared before the operation of the library apparatus.