Abstract: A transformer made of a multilayer construction in which plural spiral primary-side coils of thin plate and plural spiral secondary-side coils of thin plate are layered in turn. The primary-side coils of the multilayer construction are connected each other, the secondary-side coils of the multilayer construction are connected each other, an upper shielding layer of thin plate is disposed on the uppermost layer of the multilayer construction, and a lower shielding layer is disposed under the lowermost layer of the multilayer construction.