The invention provides a manual breast pump which can be disassembled and assembled easily for cleaning purposes, and which can readily modify a negative pressure during expression of milk generated by a lever-type operating section. A breast pump having an accommodating vessel for collecting breast milk, a breast pump main body, and an operating section attached to the breast pump main body and for deforming a negative pressure generating member installed on the breast pump main body, wherein the operating section has a lever form and includes an engagement opening as an engaged section for engaging with an engaging section provided on the breast pump main body, and the engagement opening is selectively engaged with engaging sections in a plurality of positions provided midway on an extending section erected in a pillar shape as one portion of the negative pressure generating member.