Disclosed are: a method for treating osteoporosis using PTH that is highly safe and has high effect/efficacy; a method for inhibiting/preventing bone fracture using PTH that is highly safe; and a medicinal agent for use in each of the aforementioned methods.Specifically disclosed is a medicinal agent comprising PTH as an active ingredient, which is characterized in that PTH is administered once a week at a unit dose of 100 to 200 units in each of the aforementioned methods.