To provide a bus system allowing a bus master to know completion of writing though using a memory controller not having a function notifying the bus master about the completion of the writing of data into a memory.

This bus system 1 comprises: a plurality of buses 11a, 11b; bridges 12a, 12b connecting the buses 11a, 11b; the memory 13 storing the data; the memory controller 14 directly accessing the memory 13; the bus master 15 requiring the writing or reading of the data; and a writing completion notifying device 16. The writing completion notifying device 16 transmits the writing requirement from the bus master 15 to the memory controller 14, issues the reading requirement with a writing address designated by the writing requirement as a reading address, and imparts writing completion notification to the bus master at the time point when receiving reading completion notification from the memory controller 14.