Provided by the invention is a non-halogen flame-retardant thermoplastic resin composition not requiring crosslinking with a peroxide, having excellent in moldability, and moreover, having high flame-retardancy to pass the test for V-0 grade of the UL-94. standards The non-halogen flame-retardant thermoplastic resin composition comprises, as a uniform blend: (A) 100 parts by mass of a thermoplastic resin other than polycarbonate and polyphenylene ether resins, (B) 10 to 300 parts by mass of an inorganic powder, (C) 1 to 50 parts by mass of an organopolysiloxane having a specified structure, and (D) 0.01 to 10 parts by mass of an organic compound having a specified structure.