To provide a pickling device capable of shortening pickling time with a simple piece of equipment.

A pickling device is provided with upstream side electrodes 5a, 5b to run the current in the longitudinal direction of a steel strip traveling in the pickling solution in a pickling tank 2, downstream side electrodes 6a, 6b provided with the prescribed intervals from the upstream side electrodes, an electric magnet 7 to generate the magnetic field in the width direction of the steel strip between these electrodes, means 14, 15 to measure the width and the thickness of the steel strip provided on the pickling tank inlet side, an operator to calculate the natural frequency of the steel strip between the electrodes, and a frequency controller of the alternating current.