A control device (30) for an automatic transmission (13) can be set to a first control mode and a second control mode that control the transmission ratio (SR) of the transmission (13). The control device (30) in the second control mode automatically changes the transmission ratio (SR). The control device (30) recognizes an index value and the upper limit speed (Lim) of the speed (Nout) of a transmission output shaft (23). When an operation member (22) is operated in order to increase the transmission ratio (SR), the control device (30) in the first control mode permits a change in the transmission ratio (SR) if the index value is less than or equal to the upper limit speed (Lim). The control device (30) has a setting section (S13) for setting the upper limit speed (Lim). When the control device (30) is in the first control mode and if the operation member (22) is operated in order to increase the transmission ratio (SR), the setting section (S13) sets the upper limit speed (Lim) based on vehicle acceleration (AR).