The present invention relates to a serotonin 5-HT2C receptor activator containing a compound represented by the formula wherein ring A is a 5- or 6-membered aromatic heterocycle optionally having substituent(s), and ring B is a 7- to 9-membered ring optionally having substituent(s) other than an oxo group wherein the combination of m and n (m,n) is (1,2), (2,1), (2,2), (3,1), (3,2) or (4,1), or a salt thereof or a prodrug thereof, and a fused heterocyclic compound having a serotonin 5-HT2C receptor activating action and the like.