Preheating and warming apparatus for use with vehicles comprising an outer housing provided with a clean air inlet port, a clean air outlet port and an exhaust gas outlet port, an inner housing having the interior thereof divided by a partition into a clean air introducing chamber and a combustion chamber, a fan motor disposed in the clean air introducing chamber and mounting a combustion fan on one of two output shafts of the fan motor, a sucking fan mounted on the other output shaft of the fan motor and disposed in the vicinity of the clean air inlet port of the outer housing, fuel injection means secured to the partition wall, a baffle plate disposed adjacent to the fuel injection means in the combustion chamber, a coiled water heating tube disposed in the combustion chamber, and radiation fins secured to the outer peripheral surface of the portion of the inner housing defining the combustion chamber, said components constituting a combustor for effecting combustion of liquid fuel to generate heat, said heat being used for heating air and water adapted to be supplied to a cabin and other accessories of the vehicle to heat them up.