The purpose of the present invention is to provide a solid preparation which contains a 4,5-epoxymorphinan derivative or a pharmacologically acceptable acid addition salt thereof, and which is stable against light without requiring a light-shielding coating. Provided by the present invention is a solid preparation that contains an active ingredient comprising a 4,5-epoxymorphinan derivative represented by formula (II) or a pharmacologically acceptable acid addition salt thereof, and at least one type of stabilizing agent selected from the group consisting of n-propyl gallate, sodium bisulfite, dibutylhydroxytoluene, butylated hydroxyanisole, tocopherol, and D-isoascorbic acid, wherein: the weight of the active ingredient accounts for 0.00001-0.01 wt% of the weight of the solid preparation； and the weight of the stabilizing agent accounts for 0.005-5 wt% of the weight of the solid preparation.
