To inexpensively and stably supply a derivative having a 2-acylaminopyridine configuration represented by Formula (I) in an amount required as a pest controlling agent, the present invention provides a process of producing a compound represented by Formula (B) by acylating a 2-positioned amino group of a compound represented by Formula (A) by using an acylation agent [where, Ar is a phenyl group or a 5-6 membered hetero ring, R