Provided are an aromatic vinyl polymer resin composition capable of being molded into resin foam sheets having good surface smoothness and glossiness well balanced with the mechanical strength thereof even when the expansion ratio in molding is increased, and resin foam sheets and containers of the composition. The resin composition comprises (A) from 80 to 98% by mass of an aromatic vinyl polymer resin having a weight-average molecular weight measured through GPC of from 200,000 to 400,000, a ratio of weight-average molecular weight to number-average molecular weight ranging from 2.2 to 3.6, a number of branches of from 0.1 to 1.0 in one molecule having an absolute molecular weight of 1,190,000 measured through GPC-MALLS, and a melt flow rate of from 1.5 to 3.5 g/10 min, and (B) from 2 to 20% by mass of a styrene-diene block copolymer or its hydrogenate. This is molded into a resin foam sheet through extrusion foaming, and the sheet is thermoformed into containers.