Provided herein may be a storage device and a method of operating the storage device. A memory device may include a memory cell array including a plurality of memory cells, a peripheral circuit configured to perform an operation on memory cells selected from among the plurality of memory cells, a voltage variation detector configured to generate voltage variation information indicating whether a voltage variation has occurred in a supply voltage during performance of the operation, a power register configured to store the voltage variation information, a status register configured to store status information indicating an operating status of the memory device, and a register output controller configured to update the status information provided from the status register based on the voltage variation information.