Method for producing urethane foam

The present invention is to provide a method for efficiently producing polyurethane foam having a fine uniform cell structure. The method for producing the polyurethane foam by a mechanical froth method involves a process for mechanically stirring a urethane-forming liquid composition containing a polyol and an isocyanate in an inert gas atmosphere in a first stirring mixer to disperse the inert gas in the liquid composition and to prepare a froth-shaped raw material, transferring the froth-shaped composition to a second stirring mixer, further mechanically stirring the transferred froth-shaped composition and extruding the froth-shaped composition from the second stirring mixer. The number (r1) of revolution of a rotor at the stirring by the first stirring mixer, and the number (r2) of revolution of a rotor at the stirring by the second stirring mixer are 200-1,500 rpm and 240-3,000 rpm respectively, and the ratio (r2/r1) of the numbers of the revolution is 1.2-5.0.