PURPOSE: To facilitate a finish work with high efficiency and accuracy by providing an electrolytic polishing device for a nozzle body of a fuel injection valve with a jig assembly, a needle electrode, an electrolyte supply means, a means for determining the working conditions according to the amount of working liquid and a controller.

CONSTITUTION: When a nozzle body 1 to be worked is inserted into a jig assembly 19 of a working device, the fore end of a needle electrode 15 penetrates the center of injection port 2 at the same time with a gap spaced with an equal distance from the circumference. When an electrolytic supply means works according to a command of a controller, electrolyte flows the gap between the electrode 15 and the injection port 2 of the nozzle body 1 surrounding it. The flow amount thereof is measured by a flow detection means and thus the size of the gap 28 is made clear from the level of resistance given thereto. The flow thereof is then compared with that determined by measurement carried out preliminarily on that of a normal injection valve to calculate the difference. The difference is thereafter compared with an allowable value, and when it is in the allowable range the process of electrolytic polishing is terminated.