Provided is a power supply device capable of improving workability during assembly and mounting. Accommodating a power source side connector by a cylindrical portion of a case makes a portion where the power source side connector of the harness is provided not pulled out to the outside of the case. Thus the workability at the time of assembling the power feeding device itself can be improved. Also, it is unnecessary to dispose the power source side connector where the passenger unlikely steps on, and simply mating the mating connector with the source side connector makes the workability at the time of mounting the power supply device on the vehicle improved.