A transmission device for a hybrid vehicle including a motor and an internal combustion engine which serve as driving sources, the transmission device comprising: a main shaft; a counter shaft; a plurality of shift gear rows (21 to 32) each including a fixed side gear (21, 23, 25, 27, 29, 31) fixed on one of the main shaft and the counter shaft, and a movable side gear (22, 24, 26, 28, 30, 32) disposed to be rotatable with respect to the other of the main shaft and the counter shaft, and each constituting one of a plurality of shift stages; a plurality of shift dog clutches (34, 36, 38) each arranged to selectively engage the movable side gear (22, 24, 26, 28, 30, 32) of one of the shift gear rows (21 to 32) with the other of the main shaft and the counter shaft; a main clutch disposed between the internal combustion engine and the main shaft; a first motor gear disposed to be rotatable with respect to a motor output shaft connected to the motor, and constantly interlocked with the main shaft; a second motor gear disposed to be rotatable with respect to the motor output shaft, and constantly interlocked with the counter shaft; a motor dog clutch arranged to selectively engage one of the first motor gear and the second motor gear with the motor output shaft; and a controller configured to control actuations of the shift dog clutches (34, 36, 38), the main clutch, and the motor dog clutch, wherein the first motor gear is engaged with the fixed side gear (21, 23) of one of the shift stages which is fixed on the main shaft; the second motor gear is engaged with the fixed side gear (25, 27, 29, 31) of one of the shift stages which is fixed on the counter shaft; and characterized in that when the vehicle travels in the same direction, a driving direction of the motor at an engagement of the first motor gear is opposite to a driving direction of the motor at an engagement of the second motor gear. a main shaft; a counter shaft; a plurality of shift gear rows (21 to 32) each including a fixed side gear (21, 23, 25, 27, 29, 31) fixed on one of the main shaft and the counter shaft, and a movable side gear (22, 24, 26, 28, 30, 32) disposed to be rotatable with respect to the other of the main shaft and the counter shaft, and each constituting one of a plurality of shift stages; a plurality of shift dog clutches (34, 36, 38) each arranged to selectively engage the movable side gear (22, 24, 26, 28, 30, 32) of one of the shift gear rows (21 to 32) with the other of the main shaft and the counter shaft; a main clutch disposed between the internal combustion engine and the main shaft; a first motor gear disposed to be rotatable with respect to a motor output shaft connected to the motor, and constantly interlocked with the main shaft; a second motor gear disposed to be rotatable with respect to the motor output shaft, and constantly interlocked with the counter shaft; a motor dog clutch arranged to selectively engage one of the first motor gear and the second motor gear with the motor output shaft; and a controller configured to control actuations of the shift dog clutches (34, 36, 38), the main clutch, and the motor dog clutch, wherein the first motor gear is engaged with the fixed side gear (21, 23) of one of the shift stages which is fixed on the main shaft; the second motor gear is engaged with the fixed side gear (25, 27, 29, 31) of one of the shift stages which is fixed on the counter shaft; and characterized in that when the vehicle travels in the same direction, a driving direction of the motor at an engagement of the first motor gear is opposite to a driving direction of the motor at an engagement of the second motor gear.