A transmission apparatus of an all-terrain vehicle includes: a non-stage transmission; a forward and backward movement switching device capable of switching to a forward movement position, a neutral position, or a backward movement position; and a shift operation device of rotary type for switching forward and backward movement disposed on a handle bar at a position adjacent to a handle grip. The shift operation device includes a rotary member for a shift operation and a locking mechanism for locking the rotary member so as not to move toward at least a position for backward movement from a position for neutral. The locking mechanism is configured to be handled by a hand griping the handle grip to make the locking mechanism unlocked.