To restrain manufacturing cost by downsizing a multiple-output power supply unit installed in an image forming device or the like.

This power supply device comprises a first voltage generating means 1 for generating a first DC voltage Out1 from a source power voltage, and at least one second voltage generating means 2 for forming a second DC voltage Out2 from the source power voltage and the first DC voltage. The second DC voltage includes the superimposed first DC voltage. The first voltage generating means includes first control means 1-1, 1-2, 1-8, 1-9 for maintaining the first DC voltage at a voltage level corresponding to an instruction from the outside. The second voltage generating means includes second control means 2-1, 2-2, 2-8, 2-9 for maintaining the second DC voltage at a voltage level corresponding to an instruction from the outside.