Bus transfer efficiency is improved in bus communication that uses a shared memory, based on a communication origin master 101 selectively using an arbitration completion notification signal and a memory access completion notification signal. Based on the arbitration completion notification signal, the communication origin master 101 issues a command issue permission signal to the communication destination master 102, and the communication destination master 102 generates and issues a command for accessing the shared memory 12. Based on the memory access completion notification signal, the communication origin master 101 issues a command issue permission signal to the communication destination master 102, and the communication destination master 102 generates and issues a command for accessing the shared memory 12.