A transformer is provided, including a core, a primary conductor, a magnetic member, and a secondary conductor. The core includes a central pillar and at least one lateral pillar. An accommodating space is formed between the central pillar and the lateral pillar. The primary conductor, the magnetic member, and the secondary conductor are disposed in the accommodating space. The primary conductor surrounds the central pillar. The magnetic member surrounds the primary conductor, and the secondary conductor surrounds the magnetic member. The magnetic member is disposed between the primary conductor and the secondary conductor, and is flexible.