Abstract: A transactional file system capable of realizing atomic update of plural files by transactions. In the transactional file system, a log entry containing information for validating all updates made by transaction collectively on a stable memory device, is generated for one or more files updated on a buffer region by the transaction since a start of a processing of the transaction until a commit of the transaction. Then, the log entry is written into the stable memory device at a time of the commit of the transaction.