Memory system, storage device, and method for controlling memory system

To suppress the degradation of memory cells in a non-volatile memory. A read processing unit performs a read process for reading read data from each of a plurality of memory cells on the basis of a first threshold. An error detection unit detects presence or absence of an error in the read data and specifies memory cells in which the error is present among the plurality of memory cells. A re-read processing unit performs a re-read process for reading data, as re-read data, from the specified memory cells on the basis of a second threshold different from the first threshold. A refresh processing unit rewrites, for a memory cell of which the re-read data has a different value from the read data among the specified memory cells, data with the re-read data as a refresh process.