A disk array apparatus improves scalability, performance such as data transfer between different kinds of I/Fs, and maintainability and reliability about boards/PKs configuring the DKC and about a DKC configuration obtained by interconnecting them. The DKC in the disk array apparatus is configured by interconnecting mix PKs each including a base PK and a functional PK which is hierarchically connected to the base PK and on which individually separate functions are mounted. The base PK coexists with and is connectable to a plurality of different I/F-PKs, and includes an intra-package interconnection network for communicating between the functional PKs and with the DKC, and further has a processor interconnection network. The DKC performs a data transfer processing by using the functional PK and the base PK.