Novel heterocyclic compounds shown by the formula ##STR1## wherein Het represents a 5-membered or 6-membered heterocyclic group which may have substituent(s); Z represents a sulfur atom or oxygen atom; X represents an oxygen atom or the unsubstituted or substituted imino group shown by N--R.sub.1 (wherein R.sub.1 is a hydrogen atom, a lower alkyl group, a cyano group, an unsubstituted or alkyl substituted carbamoyl group, an unsubstituted or lower alkyl substituted thiocarbamoyl group, or a lower alkanoylamino group); Y represents a hydrogen atom, a lower alkyl group which may have substituent(s), a cycloalkyl group of 3-6 carbon atoms, a lower alkenyl group, a lower alkynyl group, an aryl group which may have substituent(s), an aralkyl group which may have substituent(s), a hydroxyl group, a cyano group, a carbamoyl group, an amidino group, an alkanoyl group which may have been substituted by halogen atom(s), an alkanoylamino group, an arylcarbonylamino group, an alkylamino group, an arylamino group, an arylsulfamoyl group, a lower alkoxycarbamoyl group, or an oxamoylamino group; and m and n represent an integer of 1-3; when X is N--R.sub.1, said X and Y may combine with each other to form a 5-membered or 6-membered heterocyclic ring containing 2-3 nitrogen atoms which may have substituent(s), and the pharmacologically acceptable acid addition salts thereof.The compounds of this invention are useful as gastric acid secretion inhibitors.