Abstract: The present invention aims to provide novel compounds represented by formula [I] or pharmaceutically acceptable salts thereof: which are useful for prevention or treatment of diseases such as schizophrenia, Alzheimer's disease, cognitive impairment, dementia, anxiety disorders (e.g., generalized anxiety disorder, panic disorder, obsessive-compulsive disorder, social anxiety disorder, post-traumatic stress disorder, specific phobias, acute stress disorder), depression, drug dependence, convulsion, tremor, pain, or sleep disorders, based on their inhibitory effect against glycine uptake.