The present invention provides a solid preparation wherein variation in weight is suppressed, a solid preparation wherein the active ingredient is stabilized, and a stabilization method thereof. A solid preparation containing (1) an active ingredient, (2) D-mannitol and (3) an alkaline earth metal salt selected from magnesium aluminometasilicate and calcium silicate. A method of stabilizing the. active ingredient, including adding an alkaline earth metal salt selected from magnesium aluminometasilicate and calcium silicate.