A sulfur-containing bicyclic compound of the present invention has a PAM action of GABAB. A composition containing the sulfur-containing bicyclic compound. And, a method for preventing and/or treating schizophrenia, CIAS, cognitive impairment, fragile X syndrome, autism spectrum disorder, spasticity, anxiety disorder, substance addiction, pain, fibromyalgia, or Charcot-Marie-Tooth disease by administering the sulfur-containing bicyclic compound.