An isoindazole compound of the formula (1) or a salt thereof; a method for the production thereof; and pharmaceutical use of the compound and a salt thereof, particularly as an angiotensin II antagonist and as an agent for the prophylaxis and treatment of circulatory diseases (particularly hypertension and heart failure); ##STR1## wherein Q is a heterocyclic derivative of the formula (2) or (3) ##STR2## wherein other symbols of the above formulas are as defined in the Specification. The compound and its salt show superior angiotensin II antagonism and are low toxic. Accordingly, they are useful as angiotensin II antagonists for the treatment or prophylaxis of angiotensin II-mediated diseases such as circulatory diseases of hypertension (e.g. essential hypertension, renal hypertension) and heart failure.