To obtain a foamable carbide-type flame-retardant thermosetting resin compsn. excellent in foaming properties, the strength of the foaming carbide layer, and flame retardancy by incorporating a new amine phosphate alone or in combination with a polyphosphoric acid compound.

This compsn. comprises a thermosetting resin containing an amine phosphate of formula I [n being 1 to 100; X being R1R2N(CH2)mNR3R4 R1, R2, R3 and R4 being H or 1-5C alkyl; and m being 1 to 10), piperazine or diamine containing a piperazine ring; Y being NH3, a group of formula II (Z1 and Z2 being -NR5R6 (R5 and R6 being H, C1 to C6 alkyl or methylol), hydroxyl, mercapto, 1-10C alkyl, 1-10C alkoxy, phenyl or vinyl] alone or in combination with a polyphosphoric acid compd. This compsn. is obtained by incorporating 1 to 70wt.% of the amine phosphate alone or a combination of the amine phosphate with the polyphosphoric acid compd. in a wt. ratio of 0.1 to 10.