PURPOSE: To perform overall monitoring, and positively and quickly cope with the occurrence of abnormality when it is detected by inputting waveform signals from plural constant-current regulators based on control of either circulating monitoring or concentrated monitoring.

CONSTITUTION: Plural constant-current regulators 1 supply constant currents to a load to control it, and to perform monitoring operations. Usually, circulating monitoring specified by a control circuit 5 is performed, and a selection circuit 2 selects the regulators 1 to take out waveform data in order. The data are collected by a waveform collecting circuit 3 and analyzed by a abnormality judging circuit 4. In the circuit 4, the changes in phase waveform occurring due to abnormality in load are compared to normal waveform data previously registered, to judge normality, abnormality in the load. When the load is normal, the circulating monitoring is continued, and when it is abnormal, the circulating monitoring is switched immediately by the circuit 5 to a concentrated monitoring to concentratively monitor the regulator in which abnormality is judged, and to reaffirm the abnormality judgement and grasp the abnormal state of the load. In this manner, both the overall monitoring by the circulating monitoring and the concentrated monitoring which responds to abnormality- judgement are performed.