PURPOSE: To improve the permeability of a rust preventive by pouring the rust preventive under a high pressure together with a two pack type foaming polyurethane under a low pressure into a baggy structural part of a car body.

CONSTITUTION: A foaming polyurethane principal ingredient is pressurized by a pump 2 from a principal ingredient tank 1 and after passing through a flow rate control valve 3 is mixed with a foaming agent, which is pressurized to the same pressure as the principal ingredient by a pump 5 started from a foaming agent tank 4 and is mixed with the principal ingredient after passing through a flow control valve 6. The mixing is carried out at a trigger part 8 provided with a needle valve 7 and the mixture is discharged through a flexible hose 9 from a nozzle 10. The rust preventive pressurized by a pump 12 started from a rust preventive tank 11 is discharged from a nozzle 14 through a flexible hose 13. The rust preventive is increased in flowability by the heat generated at the time of starting foaming while generating heat by the reaction of the principal ingredient with the foaming agent, penetrates to gaps or seams of iron plates and more strongly enters the seams by the volume expansion of the polyurethane at the time of foaming.