Abstract: An output shaft locking device for a multi-clutch transmission in which a plurality of rotational mechanisms, each of which is formed by arranging a clutch and a shifting mechanism is series, is provided in parallel between a rotational power input shaft and a rotational power output shaft, and an output shaft locking method. The output shaft locking device includes a locking control device which locks the rotational power output shaft by engaging a shifting gear in each of the shifting mechanisms of at least two of the rotational mechanisms, and engaging each of the clutches of the rotational mechanisms. Thus, it is possible to lock the output shaft so as to fix wheels by engaging the shifting gear without providing a lock mechanism.