Previous research has confirmed the sterilizing impact of OH radicals produced by the collapsing motion of microbubbles in water caused by shock waves. Raising the concentration of OH radicals is required for effective sterilization, but no specific method has yet been discovered. In the present study, experiments on the generation of shock waves and microbubbles by underwater electrical discharge through a metal plate were conducted to investigate the method of increasing the generation of microbubbles that contribute to the generation of OH radicals that enhance the sterilization effects. The amount of microbubbles generated by different metal plates was analyzed using visualization and image processing based on the schlieren and the shadowgraph method. And the conditions under which the amount of microbubbles generated increased form the timing and mechanism of microbubble generation was investigated, taking into account the correlation between the amount of microbubbles generated and the physical properties of the metal plate. As a result, it was suggested that the amount of microbubble creation is relative to the first underwater shock waves caused by electric discharge, vibration of the metal plate surface generated by the elastic stress waves propagation in the metal plate and the collapse motion of the vapor bubble.