PURPOSE: To simplify the detecting sections of operational conditions through common operation thereof for each line by switching the in and output of the sections.

CONSTITUTION: When the operational requirements are met in an operational condition detecting circuit 611, an operation signal 811 is produced through a contact for a selection signal 910-1a, thus closing a breaker 201 for a line 1. When the operational requirements are subsequently met in a change-over condition circuit 612, a change-over signal 812 is produced through a contact for a selection signal 910-1a, thereby opening a breaker 101. After the operation for the line 1 is completed, the contact for the signal 910-1a is opened while the contact for the signal 920-1a is closed to perform operation for the line 2. With the same operation to that for the line 1, input-output selection signals are switched in sequence to operate all breakers on the line. The same operational condition detection circuit and change-over condition circuit can be used in common to all the lines.