To achieve a remarkable reduction in time required for drying.

A drier is provided with a truck 21 movable on a surface 10 coated with a water born polishing resin composition for a floor, infrared irradiation means 25, etc., which are carried on the truck 21 to irradiate the coated surface 10 with infrared rays and blowing means 26 and 22c for blowing air to a portion irradiated with the infrared rays by the infrared irradiation means 25, etc. Thus, the direct irradiation of the coated surface with the infrared rays is made in stead of making hot air heated by infrared rays and the like contact it to reduce the loss of heating energy and moreover, enables heating thereof deep into the film thereof not alone on the surface thereof.