Novel 3-amino-4-oxo-2,3,4,5-tetrahydro-1,5-benzoxazepine derivatives of the formula ##STR1## [wherein R.sup.1 and R.sup.2 are independently hydrogen, halogen, trifluoromethyl, lower alkyl or lower alkoxy, or both jointly form tri- or tetramethylene; R.sup.3 is hydrogen, optionally substituted lower alkyl or optionally substituted aralkyl; R.sup.4 is hydrogen, optionally substituted alkyl, optionally substituted aralkyl or optionally substituted cycloalkylalkyl; Y is a carboxyl group which may be esterified or amidated; m is 1 or 2] and salts thereof.These compounds and salts thereof exhibits inhibitory activity on angiotensin converting enzyme and so forth, and are of value as an agent for diagnosis, prevention and treatment of circulatory diseases (e.g. hypertension, cardiopathy, cerebral apoploxy).