A breast pump can include a breast pump main body having a milking portion and negative pressure generating structure for generating negative pressure. The milking portion can include a shape maintaining portion and a negative pressure generating portion that serves as a part of the negative pressure generating structure and can be attached to and detached from an inner side of the shape maintaining portion. At least one end of the negative pressure generating portion on an enlarged diameter side can include a flexible diaphragm portion and a pressing portion formed when a folded-back portion of the diaphragm portion passes an imaginary line of extension of a contact portion contacting the breast to press the breast, while the other end of the negative pressure generating portion is connected to the opening/closing structure.
