A breast pump can be configured such that is can be easily dismantled for cleaning and easily re-assembled and is formed such that an operator or operating means thereof do not easily become detached during operation. The breast pump can include a storage container for storing milk, a breast pump main body, and an operator or operating means attached to the breast pump main body for deforming a negative pressure generating member attached to the breast pump main body. The operator can take the form of a lever, and can have an engaged portion that is engaged to an engagement portion on the breast pump main body side and includes an engagement opening formed on one end side of the operator. The engagement opening can include an insertion opening portion that is formed adjacent a bearing portion side and is larger than the outer form of the engagement portion, and a holding opening portion that is coextensive with the insertion opening portion but further toward the tip end side than the insertion opening portion. The holding opening can be smaller than the outer perimeter of the engagement portion.