A transformer in which the high-voltage and low-voltage coils are easily laminated when they are alternately laminated in their axial directions, improving power efficiency. The transformer includes: a high-voltage coil including a wire wound around a cylindrical winding drum of a bobbin which is provided with flanges on both ends of the winding drum; a low-voltage coil formed of a flat plate member having an open ring shape, the low-voltage and high-voltage coils being alternately laminated in their axial directions; and a cover member which has a ring plate shape and is coaxially laminated on an outside of a laminate in an axial direction. The low-voltage coil is between the high-voltage coil and the cover member, and a wall portion protruding in the axial direction from the bobbin of the high-voltage coil and a wall portion protruding in the axial direction of the cover member are alternately disposed.