Sonodynamic treatment (SDT) is a non-invasive treatment of cancer, combining ultrasound, reactive oxygen species (ROS), and sonosensitizer. When cavitation bubbles generated by ultrasound oscillate and collapse, ROS are generated due to the high temperature and high pressure inside the bubble. By generating cavitation bubbles in a target tissue, it can be treated by the cytotoxicity of ROS, which can be further enhanced by a sonosensitizer. In SDT, the small treatment region by a single shot of HIFU results in a long treatment time, which needs to be reduced by improving the efficiency of ROS generation. ROS can be visualized by the sonochemiluminescence of luminol. In this study, a polyacrylamide gel soaked with luminol solution is used as a target of ultrasonic exposure. The effect of the duty cycle of HIFU exposure on ROS generation was investigated by capturing sonochemiluminescent light emission, and high-speed photography of cavitation bubbles.