An electrophotographic copying machine including some corona dischargers each having a high voltage transformer and an abnormal condition detection device. The abnormal condition detection device includes a detection unit for detecting an output level at a secondary winding of the transformer, an input unit for inputting an input voltage to a primary winding of the transformer. A comparator is provided for comparing the output level on the detection unit with the input level on the input unit, and outputting a detection signal. A control circuit of the copying machine is responsive to the level of the detection signal for controlling the operation of the copying machine.