LINER, TEAT CUP, AND MILKING DEVICE

Provided are a liner, a teat cup, and a milking device that can further reliably and effectively curb backflow of milk to reduce the risk of infection of mastitis. The present invention provides a liner 3 for a teat cup 1 of a milking device 10, the liner 3 having a cylindrical shape and including: a bore part 3b disposed in a cylindrical shell 2 such that a space is formed between an inner surface of the shell 2 and the bore part 3b, the bore part 3b being elastically deformable between an open state and a closed state; a mouthpiece part 3a disposed at one end of the bore part 3b and closing one end of the shell 2, the mouthpiece part 3a being configured to allow a teat 50 to be inserted therethrough and being provided with a vent 3aa; a short milk tube part 3d disposed at the other end of the bore part 3b and closing the other end of the shell 2, the short milk tube part 3d allowing milk sucked from the teat 50 by the bore part 3b to flow therethrough; and a vent line 3f provided as a groove on an inner surface of the liner 3, the vent line 3f extending on the bore part from the vent 3aa.