An alarm apparatus for an automatic transmission may include a transmission control unit (TCU) controlling the automatic transmission of a vehicle, an accelerator pedal unit, a driving unit driving the accelerator pedal unit to perform a predetermined operation, and a control unit interworking with the TCU and controlling the driving unit such that the accelerator pedal unit performs the predetermined operation at a predetermined time before a speed change time, when the speed change time calculated and outputted by the TCU may be inputted to the control unit.