PURPOSE: To eliminate an open circuit condition and minimize a short circuit current at the time of switching by repeatedly a movable terminal of either of multiple relays by turns step by step to a specified terminal so that a voltage greater than that assigned to one terminal is not applied between multiple relays at all times.

CONSTITUTION: In the case a movable terminal 7a of a mechanical relay 3 of a single movement terminal type is at a terminal a1 and a movable terminal 7b of a mechanical relay 4 of a single movement terminal type is at a terminal b1, the movable 7a of the relay 3 is moved to a terminal a2 and then the movable terminal 7b of the relay 4 is moved to a terminal b2 or b3, the movable terminal 7a of the realy 3 is again moved to a terminal a3 or a4 and then the movable terminal of the relay 4 is again moved by the amount corresponding to one or two terminals. Repeating such switchings, the movable terminals 7a, 7b are moved to required input or output terminal without applying a voltage greater than that assigned to one terminal between the movable terminals 7a and 7b.