A transmission device of a vehicle using a transmission, the transmission having a reverse gear position and a 1st speed gear position arranged opposite to one another, a 2nd speed gear position and a 3rd speed gear position arranged opposite to one another, a 4th speed gear position and a 5th speed gear position arranged opposite to one another, and a 6th speed gear position, with shift blocks (B1, B2, B4, B6) configured to shift into the gear positions by a shift operation, the transmission being configured to perform a select operation and then perform the shift operation of the shift blocks (B1, B2, B4, B6) for an automatic gear shifting, the transmission device comprising: the shift blocks (B1, B2, B4, B6) including a shift block of a reverse-1st speed, a shift block of a 4th speed-5th speed, a shift block of a 2nd speed-3rd speed, and a shift block of a 6th speed arranged in a direction of the select operation; first to fourth shift levers (24a, 25a, 25b, 24b) configured to engage with the shift blocks (B1, B2, B4, B6), a select actuator (30a, 30b) configured to move the first to fourth shift levers (24a, 25a, 25b, 24b) by the select operation; a first shift actuator configured to move the first or second shift lever (24a, 25a) by the shift operation; a second shift actuator configured to move the third or fourth shift lever (25b, 24b) by the shift operation; a gear disengagement determination unit configured to determine whether a gear disengagement is made at a desired gear position when the gear disengagement and gear engagement are performed on the desired gear position by the first and second shift actuators (31a, 31b); and a drive unit configured to drive one of the first and second actuators (31a, 31b) which is used for the gear disengagement, and drive the other of the first and second actuators (31a, 31b) which is used for the gear engagement when the gear disengagement determination unit determines that the gear disengagement is made. the shift blocks (B1, B2, B4, B6) including a shift block of a reverse-1st speed, a shift block of a 4th speed-5th speed, a shift block of a 2nd speed-3rd speed, and a shift block of a 6th speed arranged in a direction of the select operation; first to fourth shift levers (24a, 25a, 25b, 24b) configured to engage with the shift blocks (B1, B2, B4, B6), a select actuator (30a, 30b) configured to move the first to fourth shift levers (24a, 25a, 25b, 24b) by the select operation; a first shift actuator configured to move the first or second shift lever (24a, 25a) by the shift operation; a second shift actuator configured to move the third or fourth shift lever (25b, 24b) by the shift operation; a gear disengagement determination unit configured to determine whether a gear disengagement is made at a desired gear position when the gear disengagement and gear engagement are performed on the desired gear position by the first and second shift actuators (31a, 31b); and a drive unit configured to drive one of the first and second actuators (31a, 31b) which is used for the gear disengagement, and drive the other of the first and second actuators (31a, 31b) which is used for the gear engagement when the gear disengagement determination unit determines that the gear disengagement is made.