A vehicle (100) includes a motor generator (MG) and an inverter (14) driving the motor generator (MG). A power source apparatus for the vehicle includes a battery (B) as an electric storage device, a step-up converter (12) stepping up a voltage of the electric storage device and supplying it to the inverter, and a controller (30) indicating a target step-up voltage in accordance with a target state of operation of the motor generator (MG) to the step-up converter (12). If it is determined that a current operation state signal of the motor generator (MG) is abnormal, the controller (30) increases the target step-up voltage to a maximum value. Preferably, the vehicle (100) further includes a resolver (20) detecting rotation speed of a rotor of motor generator (MG). The controller (30) determines that the operation state signal is abnormal if an output of the resolver (20) does not satisfy a prescribed condition.