A battery monitoring system including: plural battery cell sets; and semiconductor devices, wherein: each of the semiconductor devices includes a measuring section, a high side communication section that is supplied with a drive voltage in a first voltage range, and, when a semiconductor device is present at a higher position that operates at a higher operating voltage than the operating voltage of the semiconductor device itself when measuring a battery cell set on the high side of the battery cell set measured by the semiconductor device itself, can perform communication with the high side semiconductor device, a low side communication section, and a communication level converter; the semiconductor device at the highest stage further includes a signal level determination section; and the first voltage range of the highest stage is set to a specific voltage range narrower than the first voltage range of another of the semiconductor devices.