The present invention provides a novel compound having few side effects such as bradycardia and the like and having superior peripheral blood lymphocyte-decreasing effect. The present invention provides a 2-aminobutanol compound represented by the following formula (I) wherein R 1 is a hydrogen atom or P(=O)(OH) 2 , R 2 is an alkyl having 1 to 4 carbon atoms optionally substituted by hydroxyl group(s) or optionally substituted by halogen atom(s), R 3 is a hydrogen atom； a halogen atom； cyano； an alkyl having 1 to 4 carbon atoms optionally substituted by halogen atom(s)； or an acyl having 2 to 5 carbon atoms optionally substituted by halogen atom(s), X is an oxygen atom, a sulfur atom, carbonyl or NR 4 wherein R 4 is a hydrogen atom or an alkyl having 1 to 4 carbon atoms, Ar 1 is an optionally substituted arylene or an optionally substituted heteroarylene, and Ar 2 is an optionally substituted aryl or an optionally substituted heteroaryl, provided that when X is an oxygen atom, Ar 1 is phenylene and Ar 2 is phenyl, then the phenyl for Ar 2 should be substituted, or a pharmaceutically acceptable acid addition salt thereof, or a hydrate thereof, or a solvate thereof, as well as a production method of the above-mentioned 2-aminobutanol compound.
