To provide a method for measuring a rust-generated area of reinforcing bars in which generation of rust can be correctly measured with a small number of measurement errors and a measurement time can be shortened, and an apparatus for measuring the same.

A total periphery of the reinforcing bar is taken in a computer to obtain a reinforcing bar image 1. An area of the reinforcing bar image 1 is separated to N dots and the N dots are color developed, whereby a red data 4, a green data 5 and a blue data 6 are obtained from one dot. The green data 5 and the blue data 6 are set from a green threshold 14 and a blue threshold 15 respectively, and binarized at 8 by being compared with the thresholds. A red data 16, a green data 17 and a blue data 18 obtained by color developing (a reference numeral 13) a typical rust data 12 are inputted as a reference for recognizing rust. The image is binarized by being compared with the data 16, 17 and 18 (reference numerals 71, 72 and 73). A total area is obtained to make a comprehensive rust judgment 9 by adding dots recognized to be red by the binarization.