A power device includes a transformer, a control signal outputting unit, and a power adjusting unit. The transformer has a primary coil and a secondary coil. The control signal outputting unit variably controls a parameter value and outputs, based on the parameter value, a control signal for controlling output power from the secondary coil. The power adjusting unit receives the control signal from the control signal outputting unit and adjusts power supplied to the primary coil based on the control signal. The power adjusting unit modifies a rate of change within a range in which the parameter value can be variably controlled, the rate of change being a rate of change in the power supplied to the primary coil with respect to the parameter value.