To provide a polyurethane foam which is pinhole-free and has a desired cell size.

The method for manufacturing a polyurethane foam comprises (a) maintaining an internal pressure of a mixing chamber at 0.1-0.7 Mpa, (b) injecting an inert gas of 3-40% by volume relative to the whole raw material in the raw material transporting means under a pressure higher, by 0.2-12 Mpa, than the mixing chamber internal pressure, and (c) agitating in a mixing chamber provided with a mixer having a nozzle.