Benzoic acid compounds of the formula ##STR1## wherein each symbol is as defined in the specification, optical isomers thereof and pharmaceutically acceptable salts thereof; pharmaceutical composition comprising this compound and pharmaceutically acceptable additive; and serotonin 4 receptor agonists, gastrointestinal prokinetic agents and therapeutic agents for various gastrointestinal diseases, which comprise this compound as active ingredient. The compounds of the present invention have high and selective affinity for serotonin 4 receptor, and show agonistic effects thereon. Accordingly, they are useful medications for the prophylaxis and treatment of various gastrointestinal diseases, central nervous disorders, cardiac function disorders, urinary diseases, and the like, as well as useful anti-nociceptors for analgesic use which increase threshold of pain.