An object of the present invention is to provide [(1R,5S,6S)-6-(aminomethyl)-3-ethylbicyclo[3.2.0]hept-3-en-6-yl]acetic acid monobenzenesulfonate as a stabilized pharmaceutical solid preparation, and also to provide a method for preparing the stabilized pharmaceutical solid preparation. The object can be attained by a pharmaceutical solid preparation comprising [(1R,5S,6S)-6-(aminomethyl)-3-ethylbicyclo[3.2.0]hept-3-en-6-yl]acetic acid monobenzenesulfonate which is compound represented by the following formula (I) in combination with (i) one or two or more components selected from the group consisting of D-mannitol, lactose, corn starch, and crystalline cellulose, (ii) carmellose calcium, and (iii) colorants.
