A positive side main contactor serving as a contact switching device on the positive side, which is connected between a positive electrode terminal of a battery pack and a high potential input terminal of an inverter, and a negative side main contactor serving as a contact switching device on the negative side, which is connected between a negative electrode terminal of the battery pack and a low potential input terminal of the inverter, are arranged so that moving contacts of these are moved forward and backward in directions that are different from each other, e.g. by 90 degrees. Thus, a situation in which the two main contactors are simultaneously turned ON upon external impact can be avoided, and consequently, it is possible to achieve the same impact resistance as was previously possible with a smaller spring force than was previously required. Therefore, it is possible, for example, to reduce the number of turns of the winding in an electromagnetic coil of each of the main contactors or to reduce the winding diameter. The size and the cost of the contact switching device are reduced while maintaining reliability.