Provided is a method for producing a butene polymer, comprising: a polymerization step of performing polymerization reaction by contacting a raw material component comprising 20% by mass or more of isobutene with a Lewis acid catalyst; and a distillation step of subjecting a solution to be treated containing a reaction product of the polymerization reaction and a butene oligomer added to the reaction product to distillation treatment to obtain the butene polymer, wherein an amount of the butene oligomer added is 25 parts by mass or larger with respect to 100 parts by mass of the reaction product.