A resin composition including 30 to 90% by mass of polyamide (A), 70 to 10% by mass of glass fibers (B), a copper compound (C) and a halogenated compound (D), wherein polyamide (A) has a sum of a terminal carboxyl group concentration and a terminal amino group concentration of 100 milliequivalents/kg or more and 200 milliequivalents/kg or less, the terminal carboxyl group concentration being higher than the terminal amino group concentration; glass fibers (B) have a fiber diameter of 10 to 20 μm and a weight average fiber length of 5 to 30 mm; the content of copper based on polyamide (A) is 30 ppm or more and 200 ppm or less; and the molar ratio of halogen to copper (halogen/copper) is more than 5 and not more than 25.