A hyperbranched polyether polyol obtained by a ring-opening reaction between a hydroxyalkyloxetane (a1) and a monofunctional epoxy compound (a2), wherein the polyether polyol includes a primary hydroxyl group (H1) and a secondary hydroxyl group (H2) in the molecular structure thereof, and has a number average molecular weight (Mn) of 1,000 to 4,000 and a hydroxyl value of 150 to 350 mgKOH/g.