A method and apparatus for reducing a page replacement time in a system using a demand paging technique are provided. The apparatus includes a memory management unit which transmits a signal indicating that a page fault occurs, a device driver which reads a page having the page fault from a nonvolatile memory, and a page fault handler that searches and secures a space for storing the page having the page fault in a memory. The searching and securing of the space in the memory is performed within a limited time calculated beforehand and a part of data to be loaded to the memory of the system is stored in the nonvolatile memory.