A power supply device includes a power supply circuit, a casing, a mold resin and a grounding member. The casing is conductive. At least part of a circuit portion of the power supply circuit is stored in the casing. A resin injector is formed in the casing. A mold resin is injected from the resin injector to fill the casing and enclose the circuit portion. The grounding member is conductive. The grounding member is arranged in the casing to shield the resin injector from the circuit portion while being in contact with the mold resin.