To provide a data processing system and a data processing method capable of shortening the operation time needed for address conversion.

An address conversion circuit 6 converts the virtual address VA o a processor core 4 into a mapped address MA based on estimated address mapping and accesses a memory system 8. After that, when estimated address conversion is decided as invalid, the access is discarded and an access to the memory is carried out again with a mapped address which is corrected and is of correct conversion. In such a case, the state of the core 4 is held by prolonging a processor clock signal or making the processor clock signal continue and also making the core 4 standby.