It will be necessary to propose a proper and reasonable maintenance scenario considering corrosion damages currently occurring to ensure the continued safe use of aging steel bridges in the region. However, measuring plate thickness and corrosion depth is challenging, and there are few examples of predicting corrosion progress for localized corrosion that develops within a single panel, especially when considering paintings. In this study, a maintenance scenario focusing on the repainting period is proposed for an actual deteriorated steel plate bridge. The corroded surface is measured using a 3D scanner, and FEM analysis is performed to predict corrosion progression, taking paint corrosion protection into account. FEM analysis was used to predict the increase in girder deflection due to the progression of localized corrosion damage, and comparisons were made with the results of actual bridge loading tests. The main conclusions of this study are as follows; 1) A future prediction method for locally corroded steel plates was presented, utilizing a 3D scanner in combination with a prediction model for corrosion progression that takes paint corrosion protection into account. Some examples of specific maintenance and management scenarios were also provided. 2) The probability distribution for the decrease in the attack factor and the determination of the corrosion area were decided after analyzing the form of localized corrosion and the current causes of that corrosion. 3) The maximum deflection of the main girder in its current condition, estimated from the load-bearing test results and analysis, was confirmed to decrease as corrosion progresses. Furthermore, the maximum deflection of the existing main girder, estimated from the results of load-bearing tests and analyses, does not surpass the deflection limit specified in JSHB standards.