A memory device includes a memory chip that stores data, and an external controller that controls the memory chip. The memory chip includes multiple memory cells configured to store data of two or more bits; and an internal controller that executes a program operation for page data including a lower and an upper page program operation, and executes a read operation for page data including a lower and an upper page read operation. The external controller includes an error correction unit that performs error correction encoding on data to be programmed into the memory cell array and performs error correction decoding on data. The internal controller outputs the read page data from the memory cell array to the external controller, regardless of whether the upper page program operation is complete or not, in the upper page read operation.