To obtain an olefin-based resin composition that, when extruded, can give a thin sheet having good mechanical properties and prevented from deteriorating in surface properties, by selecting a composition comprising a propylene resin having a specified melt tension, a specified draw speed and a specified degree of crystallinity (X-ray diffractometry) and an ethylene-based resin.

The resin composition comprising 30-90 wt.% propylene resin having a melt tension of 0.6-1.2 g, a draw speed of 30 m/min or above and a degree of crystallinity of 35-70% (X-ray diffractometry) and 10-70 wt.% ethylene-based resin is made. The value of the melt tension is limited on an account of the prevention of loose in the extrusion step and the retentivity of drawability and is desirably 0.8-1.1 g. The draw speed is limited so as to keep the spread during extrusion and to inhibit the surface of the foamed sheet from becoming sharkskin-like. The degree of crystallinity is limited on account of mechanical properties at a high temperature and the prevention of extrusion characteristics and is desirably 45-60%. The ethylene- based resin used may be a conventional ethylene (co)polymer.