PURPOSE: To exchange safely fuses, by connecting any among the lines passing the fuse of an output circuit through the contacts of a relay to an input circuit and turning the input circuit off when the fuse is blown.

CONSTITUTION: A relay 8 operates and its contacts 8a are held closed during ordinary operation; therefore, the press device is operated according to the input information to an input circuit 1. When a fuse 12 is once blown, there is no more output from an output circuit 6 and, for example, a clutch brake is turned off and the operation is interrupted. There is similarly no more input information through the contacts 8; therefore, a central arithmetic circuit 5 is turned off and the relays 7W10 of the circuit 6 are reset. Since the contacts 7aW 10a are opened as well, the inadvertent operation of a solenoid valve 11 is obviated at all even if a new fuse is inserted. The fuse is thus exchanged safely.