Provided is a stable pharmaceutical composition for oral administration containing 6-ethyl-3-({3-methoxy-4-[4-(4-methylpiperazin-1-yl)piperidine-1-yl]phenyl}amino)-5-(tetrahydro-2H-pyran-4-ylamino)pyrazine-2-carboxamide (compound A hereinafter), or a pharmacologically acceptable salt thereof, that suppresses the generation of related substances during storage. The proportion of crystals of the compound A or pharmacologically acceptable salt thereof in the stable pharmaceutical composition for oral administration is 60% or higher relative to the total weight of the compound A or pharmacologically acceptable salt thereof.本發明係提供一種抑制了於保存中生成類似物，且含有6-乙基-3-({3-甲氧基-4-[4-(4-甲基哌-1-基)哌啶-1-基]苯基}胺基)-5-(四氫-2H-吡喃-4-基胺基)吡-2-甲醯胺(以下稱作化合物A)或其製藥學上許可的鹽之安定的經口投予用醫藥組成物。前述之安定的經口投予用醫藥組成物，化合物A或其製藥學上許可的鹽之結晶之比例，相對於化合物A或其製藥學上許可的鹽之全量係60%以上。
