A coating agent containing a hydroxyalkyl cellulose in which a content of hydroxyalkoxy groups within the hydroxyalkyl cellulose is within a range of 40 to 50% by mass, preferably a coating agent containing a hydroxyalkyl cellulose in which the content of hydroxyalkoxy groups is within a range of 40 to 50% by mass and also a viscosity of 2% aqueous solution at 20° C. is within a range of 3.0 to 5.9 mPa·s； and a solid preparation coated with the coating agent.
