Provided is a performance optimization system that can identify a case where the impact on performance is large even when the number of cache misses is small. The performance optimization system includes: a required-period-of-time measurement unit that measures a required period of time concerning a to-be-observed access; a required-period-of-time table holding unit that holds a required-period-of-time table that consists of a plurality of table entries in which stored are measured values of the required period of time for each of classification regions produced by dividing a memory region for each of types based on the to-be-observed access to store a measured value of the required period of time; a table entry selection unit that makes a selection as to in which table entry, out of a plurality of table entries for each of the classification regions that make up the required-period-of-time table, the measured value of the required period of time is stored on the basis of the to-be-observed access; and a cache miss observation unit that detects the occurrence of a cache miss associated with the to-be-observed access.