In a memory controller for controlling a memory device including a memory block coupled to a plurality of word lines, the memory block including a plurality of memory cells respectively coupled to the plurality of word lines, the memory controller comprising: an operating time calculator configured to calculate program operating times taken to perform a program operation on the memory cells respectively coupled to the plurality of word lines; and an operating voltage determiner configured to determine an erase voltage to be used to erase a memory block by comparing a first program operating time, among the program operating times calculated by the operating time calculator, with the other program operating times, except the first program operating time, among the program operating times.