Warm-up apparatus for vehicle powered by external power supply

A warm-up apparatus for a vehicle including a system which charges a battery by using an external power supply is provided. The warm-up apparatus includes a heater for warming up, a current detection means, a voltage detection means and a resistance changing means. The heater is mounted in the vehicle and produces heat by receiving electric power from the external power supply. The current detection means detects an allowable current value of the external power supply. The voltage detection means detects an output voltage value of the external power supply. The resistance changing means changes an electric resistance value of the heater based on the allowable current value detected by the current detection means and the output voltage value detected by the voltage detection means.