PURPOSE: To blow out a fuse with the overcurrent and break the current application to an electric circuit by detecting the current flowing to the load with a current detecting means, in the case where a current flows to the load by the fusion of a relay contact, etc., during the stoppage of the function of load, and operating a protective relay connected to a microcomputer so as to short- circuit the load.

CONSTITUTION: In case that a current is flowing to the main current circuit due to conduction of a relay 4 by an accident, etc., a current transformer 10 detects that current, and the information is input into a microcomputer 3. The microcomputer 3 operates a protective relay circuit 12, and turns on the contact 12a. As a result, it follows that it short-circuits load 5, and an excessive current flows to a fuse 1, and the fuse 1 blows out, and the current application to the electric circuit is interrupted. Hereby, the danger can be prevented such as that the main current flows to the load and that it causes unforeseen accident by the fusion of the contact of a control relay or the like.