A high-strength and high-modulus polyolefin material can be continuously produced from a polyolefin in a powder form by feeding the polyolefin powder between a combination of endless belts disposed in an up-and-down opposing relation, compression-molding the polyolefin powder at a temperature lower than the melting point of the polyolefin powder by means of a pressing device while holding the polyolefin powder between the endless belts and conveying the same, and then rolling and stretching the resultant compression-molded polyolefin. The pressing device is constructed of pressing platens and corresponding sets of rollers, which are all accommodated within the respective endless belts. The rollers in each set are connected together, and the sets of rollers are arranged movably in an endless fashion between the respective platens and the endless belts associated therewith.