An object of the present invention is to provide an extruded propylene-based resin foam in which a average diameter of cells therein can be reduced while a high expansion ratio remains high, thereby providing an excellent insulation efficiency. The extruded propylene-based resin foam according to the present invention is extruded propylene-based resin foam that is formed by extrusion-foaming a propylene-based resin, and the extruded propylene-based resin foam has the expansion ratio of 10 or more and the average cell diameter of less than 400 μm. With this configuration, the extruded foam can have a plurality of air bubble walls therein. Thus, the extruded propylene-based resin foam can efficiently block external radiant heat, thereby realizing excellent insulation efficiency.