A power supply apparatus includes a transformer which has a primary coil and a secondary coil, a primary side semiconductor component which configures a primary side circuit connected to a side of the primary coil of the transformer, a secondary side semiconductor component which configures a secondary side circuit connected to a side of the secondary coil of the transformer, a choke coil which is connected to the secondary side semiconductor component, and a base plate on which the transformer, the primary side semiconductor component, the secondary side semiconductor component, and the choke coil are mounted. Any two of the transformer, the primary side semiconductor component, the secondary side semiconductor component, and the choke coil configure a first stacked body stacked in a normal direction of the base plate, and other two of the transformer, the primary side semiconductor component, the secondary side semiconductor component, and the choke coil configure a second stacked body stacked in the normal direction of the base plate. The power supply apparatus has a pair of first lines connecting the primary side semiconductor component and the transformer to each other, and a pair of second lines connecting the transformer and the secondary side semiconductor component to each other. The first lines and the second lines respectively have a pair of first current paths and a pair of second current paths which are arranged so as to be adjacent to each other and are configured so that currents flow in the normal direction of the base plate. At least one of the pair of the second current paths is adjacent to at least one of the pair of the first current paths in a second direction orthogonal to a first direction in which the pair of the first current paths are adjacent to each other. The first current paths and the second current paths adjacent to each other in the second direction are configured so that currents flow therethrough in directions opposite to each other.