A transformer includes an insulation member, a high voltage part, and a low voltage part, the insulation member includes a first insulator, a second insulator, and a reference plane, the high voltage part is disposed on a first side of the reference plane, the low voltage part is disposed on a second side of the reference plane, the first insulator is disposed on the reference plane, at least a portion of the second insulator is located around the high voltage part, at least one air passage is formed by the insulation member, and at least a portion of the air passage is located within a height of the high voltage part in a normal direction of the reference plane.