A transmission control device for an automatic transmission automatically changing a shift position by use of a data table that defines a gear-shift timing according to sensor information on a vehicle speed and the like, the transmission control device comprising: a cornering-state judging part judging whether its vehicle has transitioned to a cornering state from a normal running state; and a gear-shift controlling part performing gear-shift control by using a shift-up table; and a modified shift-up table generating part generating, a modified shift-up table when the vehicle is judged to have transitioned to a cornering state, the modified shift-up table making a shift-up more difficult to occur than a reference shift-up table does, wherein the gear-shift controlling part performs gear-shift control by using the reference shift-up table during the normal running state, whereas suppressing a gear shift by using the modified shift-up table instead of the reference shift-up table when the vehicle is judged to have transitioned to a cornering state, characterized in that the transmission control device further comprises: a cornering-state judgment map in which a running state of the vehicle is divided into an acceleration range, a cruise range, a deceleration range, and a throttle-off range by using a throttle opening and the vehicle speed as parameters, wherein the cornering-state judging part judges on the basis of the information on the throttle opening and the vehicle speed that the vehicle has transitioned to a cornering state from the normal running state, when the running state of the vehicle enters the cruise range from the acceleration range or when the running state of the vehicle enters the cruise range from the deceleration range. a cornering-state judging part judging whether its vehicle has transitioned to a cornering state from a normal running state; and a gear-shift controlling part performing gear-shift control by using a shift-up table; and a modified shift-up table generating part generating, a modified shift-up table when the vehicle is judged to have transitioned to a cornering state, the modified shift-up table making a shift-up more difficult to occur than a reference shift-up table does, wherein the gear-shift controlling part performs gear-shift control by using the reference shift-up table during the normal running state, whereas suppressing a gear shift by using the modified shift-up table instead of the reference shift-up table when the vehicle is judged to have transitioned to a cornering state, characterized in that the transmission control device further comprises: a cornering-state judgment map in which a running state of the vehicle is divided into an acceleration range, a cruise range, a deceleration range, and a throttle-off range by using a throttle opening and the vehicle speed as parameters, wherein the cornering-state judging part judges on the basis of the information on the throttle opening and the vehicle speed that the vehicle has transitioned to a cornering state from the normal running state, when the running state of the vehicle enters the cruise range from the acceleration range or when the running state of the vehicle enters the cruise range from the deceleration range. a cornering-state judgment map in which a running state of the vehicle is divided into an acceleration range, a cruise range, a deceleration range, and a throttle-off range by using a throttle opening and the vehicle speed as parameters, wherein the cornering-state judging part judges on the basis of the information on the throttle opening and the vehicle speed that the vehicle has transitioned to a cornering state from the normal running state, when the running state of the vehicle enters the cruise range from the acceleration range or when the running state of the vehicle enters the cruise range from the deceleration range.