In the configuration performing a data processing by a hardware processing circuit (accelerator), to provide a technology capable of improving a poorness of processing efficiency by multiple accesses to the data, the following solving means are provided. A network data processing accelerator of the present network data processing apparatus comprises processing units corresponding to each processing of an encryption/decryption, a message authentication, and a checksum, and in the data processing including a combination of each processing, accesses for the same data of the memory and the like through a bus I/F unit and the like is collected together into one time, and a pipeline processing is performed using the least common multiple of the data processing unit of each processing.