Aim: To evaluate the effectiveness of radiation protection training among medical students using X-ray equipment. Methods: Medical students attended a training class in diagnostic radiology. This training class began with a lecture on radiation protection, followed by experiments to measure the radiation dose. At the beginning and end of the training class, participants answered five-choice questions regarding the three principles of external radiation protection and the dose reduction rate of the lead apron. We also asked participants to provide free-text answers regarding what they learned from the training class and then conducted a text-mining analysis. Results: In the question regarding the three principles of external radiation protection, only 86% of students correctly answered "time" before the training class, but almost all respondents answered the question correctly after the training class. Before the training class, 81% of the students answered that the shielding rate of the lead apron was 95%, but after the training class, almost all students answered correctly that the shielding rate was 80%. Text-mining showed a co-occurrence network consisting of 10 subgraphs from the frequently occurring words. Conclusion: Having the students conduct measurement experiments on their own was effective for improving their understanding of radiation protection.