A power storage device (CA) is in parallel to a battery (B), and is connected to a power supply line (PL1) and a ground line (PL2). A service plug (SVP) internally includes a resistance (R2) and is attached to the power storage device (CA) for connecting the resistance (R2) between contacts of a relay circuit (RL1). The service plug (SVP) is a member independent of an ordinary service plug arranged at the power storage device (CA). When residual charges in the power storage device (CA) are substantially zero, an operator appropriately attaches the service plug (SVP) to the power storage device (CA) in place of the ordinary service plug. Accordingly, when the power storage device (CA) enters an overdischarged state due to a maintenance or the like of the power storage device (CA), a vehicle system to which the service plug (SVP) internally having a current limiting device is attached is started so that occurrence of a rush current can be prevented.