The invention provides the electronic judging apparatus to detect the working state of the other electric equipment without modifying it inside. The common mode noise around the electric power supplying wires of the other equipment is measured by using the special magnetic core detector attached around the power supplying wire, and the common mode noise is compared with the one measured on the non-working time after amplifying and digital signal treatment of the detected signal. As the modification of the equipment is not required, the monitoring of the working state can be available for various equipments easily and also available from a remote place by transmitting the digital treated signal on the internet communication system.