To provide an additive holder which allows an additive held inside to be discharged easily and certainly and which has a simple structure.

An additive holder comprises: an outer cylinder 2 which is inserted into a mouth part of a container body and contains the additive inside; a sealing member 3 sealing the bottom of the outer cylinder; an inner cylinder 4 which is inserted into the outer cylinder 2 with a space; a pressing part 5 closing the ceiling part of the inner cylinder; and a variable part 6 sealing between the outer cylinder 2 and the inner cylinder 4. When the pressing part 5 is pressed to press the inner cylinder 4 into the outer cylinder 2, the variable part 6 bends and deforms to follow the inner cylinder 4. In addition, the variable part 6 is pressed into the outer cylinder 2 and a tip of the inner cylinder 4, which is pressed into the outer cylinder 2 along with deformation of the variable part 6, opens the sealing member 3 and maintains a deformed state with the variable part 6 pressed into the outer cylinder 2.