A switching power supply unit is provided, which can output a DC voltage and an AC voltage with a minimized installation space. A switching circuit is provided between a winding of a transformer and a main battery. A rectifier circuit is provided between other windings of the transformer and an accessory battery. Output terminals for outputting an AC output voltage are provided at the other side of the transformer, the AC output voltage being generated based on a DC input voltage inputted from the main battery. A DC output voltage and the AC output voltage are generated based on the DC input voltage, and then outputted. The transformer is shared by a generation path of the DC output voltage and a generation path of the AC output voltage. An AC voltage input section to be inputted with the AC input voltage from external equipment may be provided at the other side of the transformer.