Provided are a drug layer applying device and a method for forming a drug layer which can quickly and easily apply or provide an appropriate amount of a drug on a surface of a medical instrument such as a balloon. A drug layer applying device that applies a drug layer on a surface of a balloon to be inserted into a living body, includes: a deformable porous body capable of holding a coating solution containing a drug and a solvent; a removal unit that is flexibly deformable and arranged alongside the porous body; and a holding base that holds the porous body and the removal unit.