A storage device including: a controller configured to be connected to an external host through an interface; a plurality of memory devices configured to store data; and a power management device configured to output an internal power voltage for an operation of the plurality of memory devices using an external power voltage received through the interface and having a flag signal pad for receiving a flag signal from the controller when the controller fails to recognize at least one of the plurality of memory devices, wherein, when the flag signal is received, the power management device changes a slope of the internal power voltage, and supplies the internal power voltage having the changed slope to the plurality of memory devices.