To provide an automatic transmission device for suppressing a fluctuation of torque to be transmitted to a shift stage at starting a vehicle while suppressing the interruption of power transmission during shift transmission.

The automatic transmission device 10 comprises a first clutch C1 having a first transmission shaft 31 and a second transmission shaft 32 which can transmit mechanical power from an input shaft 12 to a first speed gear stage 41 and a reverse travel gear stage 40, for making the input shaft 12 engageable with the first transmission shaft 31, and a second clutch C2 for making the input shaft 12 engageable with the second transmission shaft 32. The first clutch C1 or the second clutch C2 is selectively gripped for suppressing the interruption of power transmission from the input shaft 12 to an output shaft 60 during shift transmission. In this case, when the first speed gear stage 41 or the reverse travel gear stage 40 is selected, the first clutch C1 is put into a released condition to transmit the mechanical power from the input shaft 12 to the first transmission shaft 31 in a torque-converter condition.