A memory system includes a memory controller configured to control a memory device and sub-buffer memory arranged outside the memory controller. The memory controller includes a processor configured to control a memory operation for the memory device, main buffer memory that is different from the sub-buffer memory and arranged in the memory controller, and a buffer allocation circuit configured to control an allocation ratio between the sub-buffer memory and the main buffer memory. The processor sets an operation mode of the buffer allocation circuit as an operation in which the allocation ratio is fixed.