To provide a flexible polyurethane foam which is excellent in low resiliency and durability without using a plasticizer and which shows little change in hardness against a change in temperature and at the same time, has high air permeability. A process for producing a flexible polyurethane foam, which comprises reacting a polyol mixture comprising polyol (A), polyol (B) and monool (D) with a polyisocyanate compound in the presence of a blowing agent etc. at an isocyanate index of at least 90. Polyol (A) is a polyether polyol having an average of 2-3 hydroxyl groups and a hydroxyl value of from 10 to 90 mgKOH/g, obtained by ring-opening addition polymerization of an alkylene oxide to an initiator using a double metal cyanide complex catalyst; Polyol (B) is a polyether polyol having an average of 2-3 hydroxyl groups and a hydroxyl value of from 15 to 250 mgKOH/g, other than the polyol (A); and Monool (D) is a polyether monool having a hydroxyl value of from 10 to 200 mgKOH/g.