A first auxiliary switch circuit is connected to one terminal and a first terminal of a main switch circuit and generates a first auxiliary detection current. A second auxiliary switch circuit is connected to the other terminal and a second terminal of the main switch circuit and generates a second auxiliary detection current. A current adjustment detection circuit adjusts the first auxiliary detection current so that the potentials of the other terminal and the first terminal are equal and passes the first auxiliary detection current in a direction of receiving the current from the first auxiliary switch circuit and adjusts the second auxiliary detection current so that the potentials of the one terminal and the second terminal are equal and passes the second auxiliary detection current in a direction of outputting the current to the second auxiliary switch circuit, thereby generating a detection current being proportional to the output current.