Provided is a novel compound which simultaneously inhibits both NMDA receptors and ASIC1a, which are associated with neurodegenerative disease and so on, and thus is useful for the prevention and treatment of various nervous system diseases. A biguanide derivative represented by the following general formula (1), a salt thereof, or a hydrate of the derivative or the salt: wherein, X1 represents a halogen atom, R1 represents an alkyl group, an optionally substituted aryl group, or an optionally substituted aralkyl group.