The present invention provides a compound that has superior gastric acid secretion inhibitory action, ample long-lasting gastric acid secretion inhibitory action, and is able to maintain intragastric pH at a high level for an extended period of time, making it useful as a therapeutic or prophylactic agent for diseases or symptoms caused by gastric acid, as well as an active form of this compound (form to which the compound is converted in the body following administration thereof) in the form of a compound represented by general formula (1 a) (wherein R2 represents a group represented by formula (I) or the like, and R1, R3, W1 and X - are as defined in the description).
