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.