To prevent an excessive load from acting in a synchromesh part even by operating a change lever when separation of a clutch is insufficient, in a gear shift device for an automatic transmission with clutch.

In a speed changer device for an automatic transmission with clutch, in accordance with on-operation of a clutch switch 21, a clutch actuator 19 is operated, a clutch 2 is disconnected, by shift operation of a change lever 4, a power cylinder 7 of a speed changer power shift 6 is operated, a shift lever is moved. When the clutch 2 is not completely separated, a pressure of compressed air supplied to the power cylinder 7 is controlled so as to be prevented from leading to a prescribed pressure.