A therapeutic agent for fibromyalgia containing an extract from inflamed tissue inoculated with vaccinia virus as an active ingredient, use of the extract from inflamed tissue inoculated with vaccinia virus as the active ingredient for producing a medicinal composition for treating fibromyalgia, and a method of treating fibromyalgia which comprises administering a medicinal composition containing the extract from inflamed tissue inoculated with vaccinia virus as the active ingredient to a patient. The therapeutic agent containing the extract from inflamed tissue inoculated with vaccinia virus as the active ingredient is a novel therapeutic agent for fibromyalgia, no efficacious therapeutic agent for which has been known heretofore. Moreover, it is very useful as an effective drug having high safety with scarcely any side effects.