A controller includes: a processor suitable for controlling a memory device to read map data stored in a memory and read out a physical address corresponding to data requested by a host to be read; a counter suitable for obtaining reliability information on the map data stored in the memory; a determining unit suitable for activating a pre-pumping mode when reliability of the map data is poor; a deciding unit suitable for determining a first target die of a pre-pumping operation for reading the data in the activated pre-pumping mode; and a pumping unit suitable for controlling the memory device to perform the pre-pumping operation on the first target die during a background operation for reading out the physical address.