A compound of the formula wherein R1 is H or a substituent; m is 1-3; Ar is an aromatic group which may be substituted; X is a bond or a divalent straight-chain group having 1-6 atoms which may be substituted; Y is —S—, —O—, or —N(R2)— (R2 is H or a substituent group), Z is —N═ or —C(R3)═ (R3 is H or a hydrocarbon group), ring A is a benzene ring; ring B is a 5- to 7-membered ring which may be substituted, or a salt thereof is useful for eliciting a prostaglandin I2 receptor agonistic effect.