A controller includes: a counter suitable for counting a number of valid pages in each of a plurality of blocks in a memory device as first parameter values; a block selector suitable for selecting one or more first candidate blocks, the first parameter value of each of which is within a predetermined range, and selecting a victim block among the one or more first candidate blocks; and a processor suitable for controlling the memory device to read valid data stored in the victim block and program the valid data into a target block in the memory device.