A compound represented by the formula (1) [A represents a nitrogen-containing saturated ring; m represents an integer of 0 to 2; n represents an integer of 1 to 4; G.sup.1 represents hydrogen atom, chlorine atom, hydroxyl group, an alkoxy group, or amino group; G.sup.2 represents a halogen atom, hydroxyl group, cyano group, carboxy group, an alkyl group, an alkenyl group, and the like; G.sup.3 represents hydrogen atom, a halogen atom, hydroxyl group, cyano group, carboxy group, an alkyl group, an alkenyl group, and the like; G.sup.4 represents hydroxyl group, or --N(R.sup.1)(R.sup.2) (R.sup.1 and R.sup.2 represent hydrogen atom, an alkyl group, an aralkyl group, an alkenyl group, an alkynyl group, or a saturated heterocyclic group); G.sup.5 is a substituent on a ring-constituting carbon atom of A, and represents hydrogen atom, fluorine atom, or an alkyl group] or a salt thereof, or a derivative thereof that is a prodrug, which potently inhibits phosphorylation of the myosin regulatory light chain. ##STR00001##