To provide a polarity exchange system which keeps the stability of the circuit by deciding whether the load is connected.

When a power source and load are in parallel and they are of the same polarity, a straight polarity switch MSF electrically connects the power source with the load. When the current is larger than the set value, a dividing switch circuit DS is driven to shunt the current by the signal of a load current measuring device ID, and this system keeps the operation state of the circuit, and resets a series time delay circuit TD. When the power source and the load are in parallel and are of different polarity, the reversed polarity switch MSR operates after the delay time is set, and the polarity of the power source and the load is exchanged, and it becomes the same polarity of energization. When the current is larger than the set value, the dividing switch circuit DS is driven to shunt the current by the signal of the load current measuring device ID, and this system keeps the operation state of the circuit and resets the series time delay circuit TD.