An automatic transmission apparatus comprising: a plurality of first gears (52, 54, 56, 58) provided on a first shaft; a plurality of second gears (22, 24, 26, 28, 42, 44) provided on a second shaft (20a, 20b), and configured to engage with any one of the first gears to constitute gear pairs having different gear ratio; a switching mechanism (34, 40, 50, 62) configured to switch each of the gear pairs between a transmitting state in which a torque is transmitted between the first shaft and the second shaft via the gear pairs and a non-transmitting state in which the torque is not transmitted; and a gear control unit configured to control the switching mechanism while the vehicle is stopped, and switch at least two gear pairs to the transmitting state, wherein the switching mechanism includes: a clutch ring supported so as to be rotatable about an axis of at least one of the first shaft and the second shaft (20a, 20b) and configured to concentrically fix the first gears (52, 54, 56, 58) or the second gears (22, 24, 26, 28, 42, 44) so as to be rotatable; a hub fixed to the first shaft or the second shaft (20a, 20b) configured to support the clutch ring; a sleeve configured to fit the hub so as to be movable on the first shaft or the second shaft (20a, 20b) having the hub fixed thereto in an axial direction; and a movable mechanism configured to move the sleeve in the axial direction, and the clutch ring is provided so as to project toward the sleeve and includes dog teeth capable of engaging with a spline formed on the sleeve by the movement of the sleeve in the axial direction, characterized in that at least one of gears (52, 54, 56, 58, 22, 24, 26, 28, 42, 44) which constitute the gear pairs is rotatable by an external supply torque when the vehicle is stopped such that, when teeth phases of the spline of the sleeve and the clutch ring are aligned and hence cannot engage with each other, the at least one of the gears (52, 54, 56, 58, 22, 24, 26, 28, 42, 44) is rotated by the external supply torque so as to allow an engagement of the spline and the teeth of the clutch ring with each other. a plurality of first gears (52, 54, 56, 58) provided on a first shaft; a plurality of second gears (22, 24, 26, 28, 42, 44) provided on a second shaft (20a, 20b), and configured to engage with any one of the first gears to constitute gear pairs having different gear ratio; a switching mechanism (34, 40, 50, 62) configured to switch each of the gear pairs between a transmitting state in which a torque is transmitted between the first shaft and the second shaft via the gear pairs and a non-transmitting state in which the torque is not transmitted; and a gear control unit configured to control the switching mechanism while the vehicle is stopped, and switch at least two gear pairs to the transmitting state, wherein the switching mechanism includes: a clutch ring supported so as to be rotatable about an axis of at least one of the first shaft and the second shaft (20a, 20b) and configured to concentrically fix the first gears (52, 54, 56, 58) or the second gears (22, 24, 26, 28, 42, 44) so as to be rotatable; a hub fixed to the first shaft or the second shaft (20a, 20b) configured to support the clutch ring; a sleeve configured to fit the hub so as to be movable on the first shaft or the second shaft (20a, 20b) having the hub fixed thereto in an axial direction; and a movable mechanism configured to move the sleeve in the axial direction, and a clutch ring supported so as to be rotatable about an axis of at least one of the first shaft and the second shaft (20a, 20b) and configured to concentrically fix the first gears (52, 54, 56, 58) or the second gears (22, 24, 26, 28, 42, 44) so as to be rotatable; a hub fixed to the first shaft or the second shaft (20a, 20b) configured to support the clutch ring; a sleeve configured to fit the hub so as to be movable on the first shaft or the second shaft (20a, 20b) having the hub fixed thereto in an axial direction; and a movable mechanism configured to move the sleeve in the axial direction, and the clutch ring is provided so as to project toward the sleeve and includes dog teeth capable of engaging with a spline formed on the sleeve by the movement of the sleeve in the axial direction, at least one of gears (52, 54, 56, 58, 22, 24, 26, 28, 42, 44) which constitute the gear pairs is rotatable by an external supply torque when the vehicle is stopped such that, when teeth phases of the spline of the sleeve and the clutch ring are aligned and hence cannot engage with each other, the at least one of the gears (52, 54, 56, 58, 22, 24, 26, 28, 42, 44) is rotated by the external supply torque so as to allow an engagement of the spline and the teeth of the clutch ring with each other.