TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The amount of phosphorus-based flame retarder (N-1) is preferably 50-200 pts. wt. (excluding 50 pts. wt.) with respect to 100 pts. wt. cyclic olefin (co)polymer (P). The phosphorus-based flame retarder (N-1) contains phosphinic acid salt. The flame retardant composition further comprises nitrogen-type flame retardant (N-2) containing nitrogen atom in structural formula, and has decomposition temperature of 100-500 degrees C. The total content of phosphorus-based flame retarder (N-1) and nitrogen-type flame retardant (N-2) is 50-500 pts. wt. (excluding 50 pts. wt.) with respect to 100 pts. wt. cyclic olefin (co)polymer (P). The flame retardant composition further contains an oxygen atom in the structural formula containing nitrogen atom of nitrogen-type flame retardant (N-2). The nitrogen-type flame retardant (N-2) is chosen from melamine cyanurate, isocyanuric acid, tris(2-hydroxyethyl)isocyanurate, triaryl isocyanurate, tris(2,3-epoxypropyl)isocyanurate, guanidine hydrochloride, guanidine nitrate, guanidine phosphate, guanidine sulfate, guanidine sulfamate, tetraboric acid guanidine, guanidine carbonate, phosphoric acid guanylurea and sulfuric acid guanylurea, preferably melamine compound chosen from melamine, melamine-melam-melem, melamine cyanurate, melamine phosphate, melamine pyrophosphate, melamine polyphosphate, melamine polyphosphate-melam-melem and melamine sulfate. The cyclic olefin (co)polymer (P) has crosslinkable group. The cyclic olefin (co)polymer (P) comprises repeating unit (A) derived from olefin of formula (I), repeating unit (B) derived from cyclic olefin of formulae (II), (III) and (IV), and repeating unit (C) derived from cyclic olefin of formulae (VI), (VII) and (VIII). The cyclic olefin of repeating unit (B) is diene chosen from 5-vinyl-2-norbornene, 8-vinyl-9-methyltetracyclo(4.4.0.12,5.17,10)-3-dodecene and dicyclopentadiene. The cyclic olefin of repeating unit (C) is bicyclo (2.2.1)-2-heptene or tetracyclo(4.4.0.12,5.17,10)-3- dodecene.R300=H or 1-29C linear or branched hydrocarbyl;u=0 or 1;v=0 or positive integer;w=0 or 1;R61-R78,Ra1,Rb1=H, halo, 1-20C alkyl, 1-20C halogenoalkyl, 3-15C cycloalkyl, or 6-20C aryl;R102,R103=H or 1-10C alkyl;or R75+R76=monocyclic ring or multi-ring;R104=H or 1-10C alkyl;t=0-10;or R75+R76,R76+R77+R77+R78=mono-cyclic ring or multi-ring;x,d=0 or 1;y,z=0-2;R81-R99=H, halo, 1-20C alkyl, 3-15C cycloalkyl, aliphatic hydrocarbyl, 6-20C aryl, or alkoxy;or R95+R92,R95+R99=mono-cyclic or polycyclic aryl (when y=z=0);R100,R101=H or 1-5C hydrocarbyl;andf=1-18.(i) R93 and R91 are coupled through direct bond or 1-3C alkylene group. Preferred Property: The absolute value of difference of decomposition temperature of cyclic olefin (co)polymer (P) and decomposition temperature of nitrogen-type flame retardant (N-2) is 180 degrees C or less.