The present invention addresses the problem of providing: a compound exhibiting excellent stability and/or solubility and the like, and further improved FLT3 inhibitory activity； and a pharmaceutical composition. The present invention provides a salt or crystal of (S,E)-N-(1-((5-(2-((4-cyanophenyl)amino)-4-(propylamino)pyrimidine-5-yl)pent-4-yne-1-yl)amino)-1-oxopropane-2-yl)-4-(dimethylamino)-N-methylbuto-2-enamide (compound A). This salt or crystal thereof exhibits excellent FLT3 inhibitory activity, and excellent properties as a drug such as storage stability, solubility, or the like； hence, said salt or crystal thereof is useful in treating a disease or a condition pertaining to FLT3. The present invention provides a pharmaceutical composition and an FLT3 inhibitor which contain this salt or the crystal thereof.
