A tail lamp unit for a motorcycle, comprising: a tail lamp bulb; a right flasher bulb disposed rightward of the tail lamp bulb; a left flasher bulb disposed leftward of the tail lamp bulb; a reflection member including: a first reflection section configured to backwardly reflect a light emitted from the right flasher bulb; a second reflection section configured to backwardly reflect a light emitted from the left flasher bulb; and a third reflection section configured to backwardly reflect a light emitted from the tail lamp bulb; a partition member made of an opaque resin and including a first partition section; a second partition section; and a hollow space positioned between the first partition section and the second partition section, the hollow space longitudinally penetrating the partition member; the first partition section disposed rearwards of the reflection member in a front-rear direction of the tail lamp unit in its mounted position on a motorcycle, the first partition section separating a first container space and a third container space, the first container space for disposing the right flasher bulb therein, the third container space for disposing the tail lamp bulb therein; and the second partition section disposed rearwards of the reflection member in a front-rear direction of the tail lamp unit in its mounted position on a motorcycle, the second partition section separating the third container space and a second container space, the second container space for disposing the left flasher bulb therein, characterized in that the partition member is produced as an individual component separated from the reflection member, and the first partition section and the second partition section are disposed either in parallel to each other or at an interval gradually backwardly reduced in a front-rear direction of the tail lamp unit in its mounted position on a motorcycle. a tail lamp bulb; a right flasher bulb disposed rightward of the tail lamp bulb; a left flasher bulb disposed leftward of the tail lamp bulb; a reflection member including: a first reflection section configured to backwardly reflect a light emitted from the right flasher bulb; a second reflection section configured to backwardly reflect a light emitted from the left flasher bulb; and a third reflection section configured to backwardly reflect a light emitted from the tail lamp bulb; a partition member made of an opaque resin and including a first partition section; a second partition section; and a hollow space positioned between the first partition section and the second partition section, the hollow space longitudinally penetrating the partition member; the first partition section disposed rearwards of the reflection member in a front-rear direction of the tail lamp unit in its mounted position on a motorcycle, the first partition section separating a first container space and a third container space, the first container space for disposing the right flasher bulb therein, the third container space for disposing the tail lamp bulb therein; and the second partition section disposed rearwards of the reflection member in a front-rear direction of the tail lamp unit in its mounted position on a motorcycle, the second partition section separating the third container space and a second container space, the second container space for disposing the left flasher bulb therein, characterized in that the partition member is produced as an individual component separated from the reflection member, and the first partition section and the second partition section are disposed either in parallel to each other or at an interval gradually backwardly reduced in a front-rear direction of the tail lamp unit in its mounted position on a motorcycle.