To provide a rust preventive method of reinforcing bars capable of forming a rust preventing film with a film thickness with a small fluctuation and a uniform film thickness by controlling the film thickness of a rust preventive material solution to be coated when the rust preventive material solution is coated by immersing the reinforcing bars for ALC.

After the reinforcing bars 1 are immersed in the rust preventive material solution 4a, the reinforcing bars 1 are pulled out while a vibration is applied by a vibrating apparatus 5, wherein the number of vibration of the vibration applied on the reinforcing bars 1 is decreased at least one time on the way of pulling out. At this instance, the film thickness of the rust preventive material coated on the reinforcing bars 1 exposed when the pulling-out is started is measured by a film thickness measuring apparatus 6, and as smaller the difference obtained between the measured film thickness and a set film thickness is, the ratio of decreasing in decreasing the number of vibration at the first time is set larger in a range of 10-90% to the initial number of vibration.