A motorcycle tail light device can have a plurality of front engagement members, provided in a front part of a tail light support stay, that enable movement of a support position of a tail light device 50 in a vehicle longitudinal direction. A plurality of rear engagement members can be, provided in a rear part of the tail light support stay, to enable movement of the support position of the tail light device in the vehicle longitudinal direction. A front engaged member can be provided in a front part of the tail light device, engaged with any one of the plurality of front engagement members. A rear engaged member cam be provided in a rear part of the tail light device, engaged with any one of the plurality of rear engagement members.