This invention relates to a control device for leak current including: a zero-order current mutual 
inductor, a primary coil, a secondary coil and a supply 
cut-off part, in which, the primary coil contains a supply line, a 
neutral line and a surface line, and the supply line passes through the zero-order current mutual-
inductor and is connected with the first 
cut-off switch, the 
neutral line passes through the mutual-
inductor and is connected with the second 
cut-off switch, one end of the surface line is contacted with the 
metal surface shell of the supply line and the 
neutral line, the other end winds the mutual-inductor and is connected with the supply line and the neutral line by resistors, a 
test line, one end of which contacts with the surface line and the other end is connected with a test switch by a 
resistor and connected with the supply line via the test switch, which can tests out leak current and earth fault current at the same time.