PURPOSE: A transformer is provided to reduce energy loss, thereby increasing the energy transfer efficiency of the transformer. CONSTITUTION: A core unit(110) winds a first wire(101) and a second wire(102). A magnetic flux concentration preventing unit(120) is placed in the core unit to prevent magnetic flux concentration. The core unit is made of a hollow part(130) and a winding part(115). The first wire and the second wire are arranged in the hollow part. A winding unit is arranged on the inner side of the hollow part. The winding unit winds the first and second wires.
