It's confusing yes, but one thing is clear - it is not a masters degree. Here is what wikpedia says:
Juris Doctor (J.D., Latin for Doctor of Jurisprudence) is a first-professional law degree typically awarded by an accredited law school in the United States to a student who has successfully completed three years of study in law. Some law schools in Hong Kong, Singapore and Australia are now awarding the degree.
The graduate-level J.D. is not equivalent to the Bachelor of Laws degree (LL.B.) awarded in a number of English-speaking countries such as the United Kingdom, New Zealand, Singapore and Australia—that LL.B. degree is an undergraduate degree requiring no prior college-level coursework, whereas a J.D. is a doctoral-level program requiring at least three years of college-level coursework for admission to the program. The J.D. is technically a first-professional doctorate rather than a research doctorate, and holders of the degree do not, by custom, take the title "Dr." in formal address or common speech.