PURPOSE: To automatically, easily and quickly switch an electronic apparatus where trouble occurs to a standby apparatus in the system where one of electronic apparatus having current/standby relations is automatically switched to the other by the fault alarm given from one electronic apparatus.

CONSTITUTION: First and second apparatus W and P which are operated as a current apparatus and a standby apparatus and have main circuits 6 mounted and have automatic switching relations and have the essentially same constitution are provided with switching circuits 1 which input an alarm signal S4w from the current apparatus W to the standby apparatus P and allow the standby apparatus P to select the main circuit 6P of this apparatus P and output its output and output a signal, which makes the main circuit 6W of the current apparatus W nonselected to stop its output, to the current apparatus W.