A power supply unit includes: a transformer; a primary component that constitutes a primary circuit connected to the transformer; a secondary component that constitutes a secondary circuit connected to the transformer; a choke coil; a base plate including the transformer, the primary component, the secondary component and the choke coil; a metal plate connected to the base plate; and a connecting member connecting the primary component and the transformer. The primary component and the transformer are laminated to constitute a first laminating body. A part of the metal plate is disposed closer to the transformer than the primary component, and the metal plate and the transformer are electrically connected by a ground line. A connection point between the ground line and the metal plate is located closer to the transformer than the primary component.