The invention provides a breast pump capable of effectively preventing the occurrence of leaking of breast milk from a milk expressing section having an enlarged diameter during expression of milk, and also effectively preventing the loss of negative pressure due to leaking. A breast pump has an accommodating vessel for collecting breast milk; a breast pump main body which generates negative pressure for expressing milk; an enlarged-diameter milk expressing section having an enlarged diameter for abutting against a breast of a user; and a shock absorbing section, at least a portion of which abuts against a breast of a user by being formed in a substantially circular trumpet shape following an opening section of the enlarged-diameter milk expressing section, wherein the shock absorbing section includes an abutting section which abuts against an areola of the user and a tight contact section which makes tight contact with the user's breast.