Provided is a heterocyclic compound that has an excellent RBP4 reducing effect and is useful as a preventive or therapeutic drug for diseases or symptoms mediated by a rise in RBP4 or by retinol supplied by RBP4. A compound represented by formula (I): [The symbols in the formula are as mentioned in the description.] or a salt of said compound has an excellent RBP4 reducing effect and is useful as a preventive or therapeutic drug for diseases or symptoms mediated by a rise in RBP4 or by retinol supplied by RBP4.
