Pyrrolo [2,3-d] pyrimidine compound or a salt thereof

Selectively with and potently inhibit JAK3, exhibit inhibitory activity against superior antiproliferative activity of human peripheral blood mononuclear cells and has an excellent oral absorbability, IL-2-induced IFN-gamma production in in vivo provide a novel compound or a salt thereof, and pharmaceutical compositions containing them. The following formula (I) (Formula 1) [Wherein, X is, -CH = CH -, - NH-, a sulfur atom or an oxygen atom; n represents an integer of 0 to 2. ] In the compound or a salt thereof.