An ECU performs a process including the steps of: acquiring a lowest temperature TBmin and a temperature TC of cooling air; acquiring a fan airflow volume; setting a cooling coefficient; calculating a resistance value Rtmin; calculating a root-mean-square value of a current; setting TBoffset1; calculating a resistance value Rtmax; calculating a temperature index Ftmax; calculating a temperature index Ftmin; calculating an evaluation function ΔF; calculating a maximum current correction gain G; and calculating a maximum current value Imax.