PURPOSE: To improve the mechanical strength of a synthetic resin and particular ly improve the heat resistant creep characteristic of a blast fan by kneading one type or two or more types of reinforcing agents consisting of specific plural types of organic substances by a specific rate into said synthetic resin which forms said blast fan.

CONSTITUTION: A blast fan, e.g., a cross flow fan 1 is formed with a synthetic resin the main component of which is AS, etc., and consists of plural end plates 2, plural partition plates 3, and plural blade parts 4 provided in between the end plates 2 and the partition plates 3. In this case, a reinforcing agent of organic substance, together with a 30 % glass fiber, is kneaded into the synthetic resin forming the fan 1. As for the reinforcing agent, a 2-benzimidazole methyl carbamate, a 2-(4-thiazoline) benzimidazole, and a tetrachloro-isophthalonitrile are prepared and one type or two or more types of, these are kneaded in by a rate of 0.2W3 %.