A flame retardant resin composition containing 1 to 100 parts by weight of (B) an organophosphorus compound (component B) presented by the following formula (1) per 100 parts by weight of (A) a resin component (component A) containing at least 60 wt% of an acrylic resin has high flame retardancy, high transparency and satisfactory physical properties.

(wherein X 1 and X 2 are the same or different, and represent alkyl groups substituted with aromatic groups represented by the following formula (2):),

(wherein AL represents a branched or linear aliphatic hydrocarbon group having 1 to 5 carbon atoms, Ar represents a phenyl group, a naphthyl group, or an anthryl group each optionally substituted, n represents an integer of 1 to 3, and Ar can be bonded to any carbon atom in AL.)