the present invention is a method of pickling of steel plate which contains silicon comprising applying ultrasonic waves of at least two types of frequencies of 28 . 0 khz or more to less than 1 . 0 mhz to an acidic cleaning solution which contains microbubbles and , in that state , dipping the steel plate which contains silicon in that cleaning solution . the present invention is a continuous pickling system of steel plate which contains silicon which is provided with at least a support part which supports the steel plate , a conveyor which makes the steel plate move , and a pickling tank which pickles the steel plate , wherein the pickling tank has means for feeding microbubbles and means for applying ultrasonic waves of at least two types of frequencies of 28 . 0 khz or more to less than 1 . 0 mhz .