To provide a real-time file system which can secure the high response performance to a higher priority process by using a cache buffer in response to the priority of a process when a file is accessed by the process.

A process control means 101 performs the generation and deletion of processes, the CPU scheduling, etc. A process priority table 102 decides the executing sequence of processes in a CPU scheduling mode. A cache control means 103 secures and opens a cache buffer. Furthermore, an active/free state list 105 is added to manage the divided cache buffers equal to the number of process priority levels and also the blocks constructing these cache buffers respectively as a pair of working and non-working block lists. In such a constitution, a cache buffer is used in response to the priority of a process when a file is accessed by the process.