(1S)-2-acetyl-1-(4-chloro-2-methoxyphenyl)-5-fluoro-1,2,3,9-tetrahydrospiro[β-carboline-4,1′-cyclopropane] can significantly suppress a decrease of a pain threshold compared to well-known TSPO antagonists, and thus can be an excellent prophylactic and/or therapeutic agent for fibromyalgia, fibromyalgia-associated diseases, and fibromyalgia-associated symptoms.