An optical track sensing device, and in particular to an optical sensor for detecting optical tracking information on a moving medium. The storage unit is formed with an enclosure for housing portable electronic devices. Errors may be classified, for example, in response to severity, and prioritized. As a result, it is possible to reduce the rate of heat generation as compared with the case when capacity adjustment is performed for all of the capacity adjustment target cells at the same time. The pumping module includes at least one submersible centrifugal pump inclined with respect to the vertical direction at an inclination of up to 85 degrees from the vertical direction, wherein a flow in said at least one pump is ascending.