A transmission comprising: a main input shaft to which a driving force from an internal combustion engine is input; a first main shaft to which the driving force of the main input shaft is selectively transmitted via a first clutch; a second main shaft arranged coaxially with the first main shaft, the driving force of the main input shaft being selectively transmitted to the second main shaft via a second clutch; a first sub-shaft and a second sub-shaft arranged in parallel to the first main shaft and the second main shaft; a first idling gear connected to the second main shaft by a first synchronization mechanism relatively rotatably supported by the second main shaft, whereby the transmission is configured such that driving force may be transmitted via the first idling gear to the first sub-shaft and the second sub-shaft; a second synchronization mechanism whereby the transmission is configured such that driving force may be transmitted from the first main shaft to the second sub-shaft via the second synchronization mechanism; a first fixed gear fixedly provided in the second sub-shaft and configured to output the driving force; a second fixed gear fixedly provided in the first main shaft; and a third fixed gear fixedly provided in the first sub-shaft, characterized in that: the third fixed gear is configured to mesh with the second fixed gear, the second fixed gear, the third fixed gear, and the second synchronization mechanism are arranged to overlap one another when viewed from a direction perpendicular to the second main shaft, and the transmission is configured such that driving force may be transmitted via the second synchronization mechanism to the second sub-shaft, either from the first main shaft or from the second main shaft. a main input shaft to which a driving force from an internal combustion engine is input; a first main shaft to which the driving force of the main input shaft is selectively transmitted via a first clutch; a second main shaft arranged coaxially with the first main shaft, the driving force of the main input shaft being selectively transmitted to the second main shaft via a second clutch; a first sub-shaft and a second sub-shaft arranged in parallel to the first main shaft and the second main shaft; a first idling gear connected to the second main shaft by a first synchronization mechanism relatively rotatably supported by the second main shaft, whereby the transmission is configured such that driving force may be transmitted via the first idling gear to the first sub-shaft and the second sub-shaft; a second synchronization mechanism whereby the transmission is configured such that driving force may be transmitted from the first main shaft to the second sub-shaft via the second synchronization mechanism; a first fixed gear fixedly provided in the second sub-shaft and configured to output the driving force; a second fixed gear fixedly provided in the first main shaft; and a third fixed gear fixedly provided in the first sub-shaft, the third fixed gear is configured to mesh with the second fixed gear, the second fixed gear, the third fixed gear, and the second synchronization mechanism are arranged to overlap one another when viewed from a direction perpendicular to the second main shaft, and the transmission is configured such that driving force may be transmitted via the second synchronization mechanism to the second sub-shaft, either from the first main shaft or from the second main shaft.