The present invention provides an attachment structure of a fuel cut-off unit (U) that is provided in a fuel tank (31) of a saddle-type vehicle (1), includes a breather passage (114) for discharging volatile fuel to the outside, and includes a valve device (50) for cutting off outflow of liquid fuel. The fuel cut-off unit (U) includes an accommodation container (100) constituted of a fitting portion (U2) which is inserted into the fuel tank (31) at the time of attachment to the fuel tank (31) and a unit exterior portion (U1) which is positioned outside the fuel tank (31). A first locking portion (105) for performing positioning at the time of attachment to the fuel tank (31) is formed in the fitting portion (U2). A penetration hole (C) penetrating from the inside to the outside such that the fitting portion (U2) is inserted therethrough is formed in the fuel tank (31). A second locking portion (F) for fixing the fuel cut-off unit (U) by causing the first locking portion (105) to be engaged from an inner side of the fuel tank is provided in a circumferential edge portion of the penetration hole (C).