To optimally assign transmission amount of alarm data transmitted on a monitoring bus by a package to be monitored.

Mounting information like a PWR alarm, etc., from each package 21 to 2n to be monitored and a transmission amount change request signal are received in a package abnormality monitoring part 11 and a data transmission-reception transmission amount setting means 10 with respect to a CPU package 1. The transmission amount is controlled by accepting the transmission amount change request signals of the monitoring object packages 21 to 2n only when a mounting condition of the monitoring object packages 21 to 2n is well and transmitting alarm information in a signal processing part 12 of the packages 21 to 2n held in a data transmitting and receiving part 4 to the monitoring bus.