Current detecting device, impedance measuring instrument and power measuring instrument

A current detector, comprising:

• a first terminal, which receives power source current;
• a second terminal, which feeds external device to an outside current;
• a third terminal, which outputs pilot current having a predefined relationship with said output current;
• a fourth terminal having reference potential;
• a first component connected between the first and second terminals;
• a first balun, which comprises the first and second terminals as a first pair of input terminals and has a first pair of output terminals connected by a first line to said first input pair of terminals;
• a second balun, which comprises said first pair of output terminals as a second pair of input terminals and has a second output pair of terminals connected by a second line to said second pair of input terminals,
• a first capacitive component, which is connected between one output terminal of said first pair of output terminals having direct-current coupling with said first terminal and said fourth terminal;
• and
• a second capacitive component, which is connected between one of the output terminals of said second pair of output terminals having direct-current coupling with said first terminal and said fourth terminal,
• wherein the other output terminal of said second pair of output terminals having direct-current coupling with said second terminal serves as the third terminal.