Switching power supply device

A switching power supply device including a plurality of power supply circuits connected to a multi-phase power supply, comprising:

• a first board including, mounted thereon, an electrical part that constitutes a filter circuit for preventing entry of noise from the power supply, an output end of the filter circuit being provided adjacent to one end in a first direction of the first board;
• a second board placed on a bottom portion of a casing that accommodates the switching power supply device, the second board including, mounted thereon, a power semiconductor that constitutes a circuit provided at a latter part of the filter circuit, an input end of the circuit provided at the latter part of the filter circuit being provided adjacent to one end in a second direction of the second board, the second direction crossing the first direction;
• and
• a third board disposed between the first board and the second board, the third board including, formed thereon, a wiring pattern that electrically connects the output end to the input end.