A power supply unit of vehicle comprises a battery (B1), power lines (a power supply line (PL1) and a ground line (SL2)), a joint (20), a charger (6) as a power supply section, an auxiliary machine load (45), a voltage sensor (13), and a controller (30). When the auxiliary machine load (45) is in an operating state, the controller (30) sends signals (CNT1, CNT2, CNT3) to the joint (20) and turns all of three system main relays (SMR1-SMR3) off. Consequently, electrical connection between the battery (B1) and the charger (6) is interrupted. Furthermore, the controller (30) generates a power command (Pchg) based on a target voltage and a detected voltage (VH) such that the voltage (VH) detected by the voltage sensor (13) is equal to the predetermined target voltage.